Sensor for blood pump

ABSTRACT

Apparatus and methods are described including a blood pump that includes an impeller, and a motor configured to drive the impeller to pump blood by rotating the impeller. The impeller is configured to undergo axial motion, in response to changes in a pressure against which the impeller is pumping. A sensor detects the axial motion of the impeller, and generates a sensor signal in response thereto. A computer processor receives the sensor signal and generates an output in response thereto. Other applications are also described.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.16/281,264 to Tuval (published as US 2019/0209758), filed Feb. 21, 2019,which is a continuation of International Application No.PCT/IB2019/050186 to Tuval (published as WO 19/138350), filed Jan. 10,2019, entitled “Ventricular assist device,” which claims priority from:

-   U.S. Provisional Patent Application No. 62/615,538 to Sohn, entitled    “Ventricular assist device,” filed Jan. 10, 2018;-   U.S. Provisional Patent Application No. 62/665,718 to Sohn, entitled    “Ventricular assist device,” filed May 2, 2018;-   U.S. Provisional Patent Application No. 62/681,868 to Tuval,    entitled “Ventricular assist device,” filed Jun. 7, 2018; and-   U.S. Provisional Patent Application No. 62/727,605 to Tuval,    entitled “Ventricular assist device,” filed Sep. 6, 2018.

All of the above-referenced US Provisional applications are incorporatedherein by reference.

FIELD OF EMBODIMENTS OF THE INVENTION

Some applications of the present invention generally relate to medicalapparatus. Specifically, some applications of the present inventionrelate to a ventricular assist device and methods of use thereof.

BACKGROUND

Ventricular assist devices are mechanical circulatory support devicesdesigned to assist and unload cardiac chambers in order to maintain oraugment cardiac output. They are used in patients suffering from afailing heart and in patients at risk for deterioration of cardiacfunction during percutaneous coronary interventions. Most commonly aleft-ventricular assist device is applied to a defective heart in orderto assist left-ventricular functioning. In some cases, aright-ventricular assist device is used in order to assistright-ventricular functioning. Such assist devices are either designedto be permanently implanted or mounted on a catheter for temporaryplacement.

SUMMARY OF EMBODIMENTS

In accordance with some applications of the present invention, aventricular assist device includes an impeller disposed upon an axialshaft, with a frame disposed around the impeller. The ventricular assistdevice typically includes a tube, which traverses the subject's aorticvalve, such that a proximal end of the tube is disposed in the subject'saorta and a distal end of the tube is disposed within the subject's leftventricle. The impeller, the axial shaft and the frame are disposedwithin a distal portion of the tube inside the subject's left ventricle.Typically, the impeller is configured to pump blood from the leftventricle into the aorta by rotating. The tube typically defines one ormore blood inlet openings at the distal end of the tube, via which bloodflows into the tube from the left ventricle, during operation of theimpeller. For some applications, the proximal portion of the tubedefines one or more blood outlet openings, via which blood flows fromthe tube into the ascending aorta, during operation of the impeller.

For some applications, the impeller includes proximal and distalbushings, and the frame includes proximal and distal bearings. The axialshaft typically passes through the proximal and distal bearings of theframe and the proximal and distal bushings of the impeller. For someapplications, (a) the proximal bushing of the impeller is coupled to theaxial shaft, such that the proximal bushing is held in an axially-fixedposition with respect to the axial shaft, and (b) the distal bushing ofthe impeller is not coupled to the axial shaft, such that the distalbushing is not held in an axially-fixed position with respect to theaxial shaft. Typically, the impeller defines a radially-constrainedconfiguration in which the impeller is introduced into the subject'sbody and a non-radially-constrained configuration in which the impelleris configured to pump blood within the subject's body. For someapplications, the impeller changes from its radially-constrainedconfiguration to its non-radially-constrained configuration by thedistal bushing sliding over the axial shaft.

Typically, the axial shaft is not held in an axially-fixed position withrespect to the proximal and distal bearings. Further typically, theventricular assist device (and/or a blood pump portion thereof) does notinclude any thrust bearing configured to be disposed within thesubject's body. For some applications, the ventricular assist deviceincludes one or more thrust bearings that are disposed outside thesubject's body, and opposition to thrust generated by the rotation ofthe impeller is provided solely by the one or more thrust bearingsdisposed outside the subject's body.

For some applications, a motor drives the impeller to pump blood fromthe left ventricle to the aorta, by rotating the impeller, and theimpeller is configured to undergo axial motion with respect to theframe, in response to the pressure difference between the left ventricleand the aorta changing. For some applications, a computer processormeasures an indication of the axial motion of the impeller. For someapplications, the computer processor derives the subject's cardiaccycle, the pressure difference between the left ventricle and the aorta,and/or left-ventricular pressure of the subject, based upon the measuredindication of the axial motion of the impeller. For some applications,the computer processor changes a rate of rotation of the impeller, atleast partially based upon the sensor signal. For example, the computerprocessor may determine left-ventricular pressure of the subject, atleast partially based upon the sensor signal, and may change a rate ofrotation of the impeller, at least partially based upon the determinedleft-ventricular pressure. For some applications, the computer processorreduces the rate of rotation of the impeller, in response to determiningthat the subject's left-ventricular pressure has decreased. For someapplications, the impeller is coupled to a magnet such that axial motionof the impeller causes the magnet to undergo axial motion, and thecomputer processor measures the indication of the axial motion of theimpeller by measuring magnetic flux generated by the magnet.

Typically, a drive cable extends from outside the subject's body to theaxial shaft, and is configured to impart rotational motion from themotor to the impeller by rotating, such that the impeller pumps bloodfrom the left ventricle to the aorta by rotating a given direction. Forsome applications, at least a portion of the drive cable includes aplurality of wires disposed in a coiled configuration that is such that,in response to the drive cable rotating in the given direction ofrotation, the plurality of wires disposed in the coiled configuration atleast partially unwind, such that the portion of the drive cableshortens axially. For some applications, an outer tube is disposedaround the drive cable, and frictional forces between the outer tube andthe drive cable are such as to typically generate debris. Alternativelyor additionally, a fluid (e.g., a purging fluid) is disposed between theouter tube and the drive cable. For some such applications, at least aportion of the drive cable is configured such that the plurality ofwires disposed in the coiled configuration are configured to pump thedebris and/or the fluid toward the proximal end of the drive cable.

For some applications, the drive cable includes a first portionconfigured to be disposed at least partially within an aortic arch ofthe subject, and a second portion configured to be disposed at leastpartially within a descending aorta of the subject, and the flexibilityof the first portion is greater than the flexibility of the secondportion. For example, the first portion of the drive cable may include afirst number of wires disposed in a coiled configuration, and the secondportion of the drive cable may include a second number of wires disposedin a coiled configuration, and the first number is lower than the secondnumber. For example, the first portion of the drive cable may includebetween 4 and 8 wires disposed in a coiled configuration, and the secondportion of the drive cable may include between 8 and 12 wires disposedin a coiled configuration.

For some applications, the impeller includes at least one helicalelongate element (and typically, three helical elongate elements), and aspring that is disposed inside of the helical elongate element, andalong an axis around which the helical elongate element winds.Typically, a film of material (e.g., silicone) is supported between thehelical elongate element and the spring. For some applications, at leastone elongate element (e.g., a string or a wire) extends from the springto the helical elongate element and is configured to maintain thehelical elongate element within a given distance from the spring.

As described hereinabove, for some applications, a frame is disposedaround the impeller. For some applications, the ventricular assistdevice includes a stator that includes a plurality of curved projectionsthat are coupled to a proximal end of the frame. Typically, thecurvature of the curved projections opposes the direction of rotation ofthe impeller. For some applications, the curvature of the curvedprojections is such that, from distal ends of the curved projections toproximal ends of the curved projections, the curved projections becomeprogressively closer to being parallel with the longitudinal axis of theframe. Typically, the curved projections comprise a plurality of curvedstruts that are integral with the frame, and a flexible material (e.g.,silicone) that extends from the curved struts. For some applications,the flexible material is shaped to define a lumen therethrough.

As described hereinabove, typically the impeller is disposed within atube (which is sometimes referred to herein as a “blood-pump tube”) thatextends from the subject's left ventricle to the subject's aorta. Forsome applications, at least one blood-pressure-measurement tube, whichdefines an opening at its distal end, extends to at least an outersurface of the blood-pump tube, such that the opening at the distal endof the blood-pressure-measurement tube is in direct fluid communicationwith the subject's bloodstream outside the blood-pump tube. A pressuresensor measures pressure of blood within the blood-pressure-measurementtube. For some applications, the blood-pressure-measurement tube isconfigured to pass along an outer surface of the blood-pump tube fromthe proximal end of the blood-pump tube until the opening at the distalend of the blood-pressure-measurement tube. Typically, theblood-pressure-measurement tube is a left-ventricular blood-pressuremeasurement tube that is configured to extend to the outer surface ofthe blood-pump tube at a location along the blood-pump tube that isconfigured to be within the subject's left ventricle proximal to theimpeller, and the pressure sensor is configured to measureleft-ventricular pressure of the subject by measuring pressure of bloodwithin the left-ventricular blood-pressure-measurement tube.

Typically, the blood-pump tube defines one or more blood inlet openingswithin the distal portion of the blood-pump tube, and one or more bloodoutlet openings within a proximal portion of the blood-pump tube. Forsome applications, the ventricular assist device includes aradially-expandable atraumatic distal tip portion configured to bedisposed within the subject's left ventricle distally with respect tothe one or more blood inlet openings. The distal tip portion istypically configured to be inserted into the left ventricle in aradially-constrained configuration, and to assume anon-radially-constrained configuration within the subject's leftventricle in which at least a radially-expandable portion of the distaltip portion is radially expanded relative to the radially-constrainedconfiguration of the distal tip portion. Typically, in itsnon-radially-constrained configuration, the radially-expandable portionof the distal tip portion separates the one or more blood inlet openingsfrom inner structures of the left ventricle, such as theinterventricular septum, chordae tendineae, papillary muscles, and/orthe apex of the left ventricle. Further typically, in itsnon-radially-constrained configuration, the radially-expandable portionof the distal tip portion separates the one or more blood inlet openingsfrom the inner structures of the left ventricle in three dimensions. Forsome applications, in its non-radially-constrained configuration, theradially-expandable portion of the distal tip portion directs blood flowfrom the left ventricle into the one or more blood inlet openings.

For some applications, in the radially-constrained configuration of thedistal tip portion, a distal region of the distal tip portion isconfigured to be least semi-rigid, and is shaped to radially convergealong a longitudinal direction toward a distal end of the distal tipportion. Typically, the ventricular assist device is configured to beinserted into the subject's body via a puncture in the subject's body.For some applications, during the insertion of the ventricular assistdevice, the distal region of the distal tip portion is configured to actas a dilator by dilating the puncture.

In general, in the specification and in the claims of the presentapplication, the term “proximal” and related terms, when used withreference to a device or a portion thereof, should be interpreted tomean an end of the device or the portion thereof that, when insertedinto a subject's body, is typically closer to a location through whichthe device is inserted into the subject's body. The term “distal” andrelated terms, when used with reference to a device or a portionthereof, should be interpreted to mean an end of the device or theportion thereof that, when inserted into a subject's body, is typicallyfurther from the location through which the device is inserted into thesubject's body.

The scope of the present invention includes using the apparatus andmethods described herein in anatomical locations other than the leftventricle and the aorta. Therefore, the ventricular assist device and/orportions thereof are sometimes referred to herein (in the specificationand the claims) as a blood pump.

There is therefore provided, in accordance with some applications of thepresent invention, apparatus including:

a blood pump configured to be placed inside a body of subject, the bloodpump including:

-   -   an impeller including proximal and distal bushings;    -   a frame configured to be disposed around the impeller, the frame        including proximal and distal bearings;    -   an axial shaft configured to pass through the proximal and        distal bearings of the frame and the proximal and distal        bushings of the impeller,    -   the proximal bushing of the impeller being coupled to the axial        shaft, such that the proximal bushing is held in an        axially-fixed position with respect to the axial shaft, and    -   the distal bushing of the impeller not being coupled to the        axial shaft, such that the distal bushing is not held in an        axially-fixed position with respect to the axial shaft, and    -   the impeller defining a radially-constrained configuration in        which the impeller is introduced into the subject's body and a        non-radially-constrained configuration in which the impeller is        configured to pump blood within the subject's body, the impeller        being configured to change from its radially-constrained        configuration to its non-radially constrained configuration by        the distal bushing sliding over the axial shaft.

In some applications, the impeller is configured to be placed inside aleft ventricle of the subject, and to pump blood from the subject's leftventricle to an aorta of the subject. In some applications, the impelleris configured to be placed inside a right ventricle of the subject, andto pump blood from the subject's right ventricle to a pulmonary arteryof the subject. In some applications, the impeller is configured to beplaced inside a blood vessel of the subject. In some applications, theimpeller is configured to be placed inside a cardiac chamber of thesubject.

In some applications, the impeller includes:

at least one helical elongate element that extends from the proximalbushing to the distal bushing;

a spring that is disposed inside of the helical elongate element, andalong an axis around which the helical elongate element winds;

a film of material supported between the helical elongate element andthe spring; and

at least one flexible elongate element extending from the spring to thehelical elongate element and configured to maintain the helical elongateelement within a given distance from the spring, the at least oneflexible elongate element being selected from the group consisting of: astring and a wire.

In some applications, the apparatus further includes a deliverycatheter,

the delivery catheter is configured to maintain the impeller in itsradially-constrained configuration during introduction of the impellerinto the subject's body,

upon the impeller being released from the delivery catheter, theimpeller is configured to self-expand to thereby cause the distalbushing to slide over the axial shaft proximally, such that the impellerassumes its non-radially-constrained configuration, and

in order to retract the impeller from the subject's body, the deliverycatheter is configured to cause the impeller to assume itsradially-constrained configuration by a distal end of the deliverycatheter and the impeller being moved with respect to one another suchthat the distal end of the delivery catheter causes the distal bushingto slide over the axial shaft distally.

There is further provided, in accordance with some applications of thepresent invention, apparatus including:

a ventricular assist device including:

-   -   an impeller configured to be placed inside a left ventricle of a        subject;    -   a frame configured to be disposed around the impeller; and    -   a motor configured to drive the impeller to pump blood from the        left ventricle to an aorta of the subject, by rotating the        impeller,    -   the impeller being configured to undergo axial back-and-forth        motion with respect to the frame, in response to cyclical        changes in a pressure difference between the left ventricle and        the aorta.

In some applications:

the impeller includes proximal and distal bushings;

the frame includes proximal and distal bearings; and

the ventricular assist device further includes an axial shaft configuredto pass through the proximal and distal bearings defined by the frameand the proximal and distal bushings of the impeller, the axial shaft:

-   -   being coupled to at least one of the proximal and distal        bushings of the impeller, such that the at least one bushing is        held in an axially-fixed position with respect to the axial        shaft, and    -   not being held in an axially-fixed position with respect to the        proximal and distal bearings.

In some applications, the ventricular assist device does not include anythrust bearing configured to be disposed within a body of the subject.

In some applications, the ventricular assist device further includes oneor more thrust bearings configured to be disposed outside a body of thesubject, and wherein opposition to thrust generated by the rotation ofthe impeller is provided solely by the one or more thrust bearingsdisposed outside the subject's body.

In some applications,

the motor is configured to drive the impeller to pump blood from thesubject's left ventricle to the subject's aorta, by rotating theimpeller in a given direction of rotation; and

the ventricular assist device further includes:

-   -   an axial shaft, the impeller being disposed on the axial shaft;        and    -   a drive cable configured to extend from outside a body of the        subject to the axial shaft, the drive cable being configured to        impart rotational motion from the motor to the impeller by        rotating, at least a portion of the drive cable including a        plurality of wires disposed in a coiled configuration that is        such that, in response to the drive cable rotating in the given        direction of rotation, the plurality of wires disposed in the        coiled configuration at least partially unwind, such that the        portion of the drive cable shortens axially.

In some applications, the apparatus further includes:

a sensor configured to detect an indication of axial motion of theimpeller, and to generate a sensor signal in response thereto; and

a computer processor configured to receive the sensor signal and togenerate an output in response thereto.

In some applications, the computer processor is configured to generatean output indicating a cardiac cycle of the subject, in response toreceiving the sensor signal. In some applications, the computerprocessor is configured to determine left-ventricular pressure of thesubject, at least partially based upon the sensor signal. In someapplications, the computer processor is configured to change a rate ofrotation of the impeller, at least partially based upon the sensorsignal.

In some applications, the computer processor is configured:

to determine left-ventricular pressure of the subject, at leastpartially based upon the sensor signal, and

to change a rate of rotation of the impeller, at least partially basedupon the determined left-ventricular pressure.

In some applications, the computer processor is configured to reduce therate of rotation of the impeller, in response to determining that thesubject's left-ventricular pressure has decreased.

In some applications, the apparatus further includes:

a magnet, the impeller being coupled to the magnet such that axialmotion of the impeller causes the magnet to undergo axial motion;

a sensor configured to detect magnetic flux generated by the magnet, andto generate a sensor signal in response thereto; and

a computer processor configured to receive the sensor signal and togenerate an output in response thereto.

In some applications, the computer processor is configured to generatean output indicating a cardiac cycle of the subject, in response toreceiving the sensor signal. In some applications, the computerprocessor is configured to determine left-ventricular pressure of thesubject, at least partially based upon the sensor signal. In someapplications, the computer processor is configured to change a rate ofrotation of the impeller, at least partially based upon the sensorsignal.

In some applications, the computer processor is configured:

to determine left-ventricular pressure of the subject, at leastpartially based upon the sensor signal, and

to change a rate of rotation of the impeller, at least partially basedupon the determined left-ventricular pressure.

In some applications, the computer processor is configured to reduce therate of rotation of the impeller, in response to determining that thesubject's left-ventricular pressure has decreased.

In some applications:

the impeller includes proximal and distal bushings;

the frame includes proximal and distal bearings;

the ventricular assist device further includes an axial shaft configuredto pass through the proximal and distal bearings of the frame and theproximal and distal bushings of the impeller;

the impeller is coupled to the axial shaft such that the impeller causesthe axial shaft to undergo axial back-and-forth motion with respect tothe proximal and distal bearings of the frame.

In some applications, the axial shaft is configured to clean interfacesbetween the axial shaft and the proximal and distal bearings of theframe, by undergoing the axial back-and-forth motion with respect to theproximal and distal bearings of the frame. In some applications, theaxial shaft is configured to reduce a build-up of heat at interfacesbetween the axial shaft and the proximal and distal bearings of theframe, by undergoing the axial back-and-forth motion with respect to theproximal and distal bearings of the frame, relative to if the axialshaft did not undergo the axial back-and-forth motion with respect tothe proximal and distal bearings of the frame.

There is further provided, in accordance with some applications of thepresent invention, apparatus including:

a blood pump including:

-   -   an impeller including proximal and distal bushings, and        configured to pump blood through the subject's body;    -   a frame configured to be disposed around the impeller, the frame        including proximal and distal bearings;    -   an axial shaft configured to pass through the proximal and        distal bearings of the frame and the proximal and distal        bushings of the impeller, the axial shaft:        -   being coupled to at least one of the proximal and distal            bushings of the impeller, such that the at least one bushing            is held in an axially-fixed position with respect to the            axial shaft, and        -   not being held in an axially-fixed position with respect to            the proximal and distal bearings.

In some applications, the blood pump does not include any thrust bearingconfigured to be disposed within the subject's body. In someapplications, wherein the blood pump further includes one or more thrustbearings configured to be disposed outside the subject's body, andwherein opposition to thrust generated by the rotation of the impelleris provided solely by the one or more thrust bearings disposed outsidethe subject's body.

In some applications, the apparatus further includes:

a sensor configured to detect an indication of axial motion of theimpeller, and to generate a sensor signal in response thereto; and

a computer processor configured to receive the sensor signal and togenerate an output in response thereto.

In some applications, the computer processor is configured to generatean output indicating a cardiac cycle of the subject, in response toreceiving the sensor signal. In some applications, the computerprocessor is configured to determine left-ventricular pressure of thesubject, at least partially based upon the sensor signal. In someapplications, the computer processor is configured to change a rate ofrotation of the impeller, at least partially based upon the sensorsignal.

In some applications, the computer processor is configured:

to determine left-ventricular pressure of the subject, at leastpartially based upon the sensor signal, and

to change a rate of rotation of the impeller, at least partially basedupon the determined left-ventricular pressure.

In some applications, the computer processor is configured to reduce therate of rotation of the impeller, in response to determining that thesubject's left-ventricular pressure has decreased.

In some applications, the apparatus further includes:

a magnet, the impeller being coupled to the magnet such that axialmotion of the impeller causes the magnet to undergo axial motion;

a sensor configured to detect magnetic flux generated by the magnet, andto generate a sensor signal in response thereto; and

a computer processor configured to receive the sensor signal and togenerate an output in response thereto.

In some applications, the computer processor is configured to generatean output indicating a cardiac cycle of the subject, in response toreceiving the sensor signal. In some applications, the computerprocessor is configured to determine left-ventricular pressure of thesubject, at least partially based upon the sensor signal. In someapplications, the computer processor is configured to change a rate ofrotation of the impeller, at least partially based upon the sensorsignal.

In some applications, the computer processor is configured:

to determine left-ventricular pressure of the subject, at leastpartially based upon the sensor signal, and

to change a rate of rotation of the impeller, at least partially basedupon the determined left-ventricular pressure.

In some applications, the computer processor is configured to reduce therate of rotation of the impeller, in response to determining that thesubject's left-ventricular pressure has decreased.

In some applications, the impeller is configured to pump blood from afirst location within the subject's body to a second location within thesubject's body, and the impeller is configured to undergo axialback-and-forth motion with respect to the frame, in response to cyclicalchanges in a pressure difference between the first location and thesecond location. In some applications, the impeller is configured topump blood from a left ventricle of the subject to an aorta of thesubject, and the impeller is configured to undergo axial back-and-forthmotion with respect to the frame, in response to cyclical changes in apressure difference between the left ventricle and the aorta. In someapplications, the impeller is configured to pump blood from a rightventricle of the subject to a pulmonary artery of the subject, and theimpeller is configured to undergo axial back-and-forth motion withrespect to the frame, in response to cyclical changes in a pressuredifference between the right ventricle and the pulmonary artery. In someapplications, the impeller is configured to pump blood from a rightatrium of the subject to a right ventricle of the subject, and theimpeller is configured to undergo axial back-and-forth motion withrespect to the frame, in response to cyclical changes in a pressuredifference between the right atrium and the right ventricle. In someapplications, the impeller is configured to pump blood from a vena cavaof the subject to a right ventricle of the subject, and the impeller isconfigured to undergo axial back-and-forth motion with respect to theframe, in response to cyclical changes in a pressure difference betweenthe vena cava and the right ventricle. In some applications, theimpeller is configured to pump blood from a right atrium of the subjectto a pulmonary artery of the subject, and the impeller is configured toundergo axial back-and-forth motion with respect to the frame, inresponse to cyclical changes in a pressure difference between the rightatrium and the pulmonary artery. In some applications, the impeller isconfigured to pump blood from a vena cava of the subject to a pulmonaryartery of the subject, and the impeller is configured to undergo axialback-and-forth motion with respect to the frame, in response to cyclicalchanges in a pressure difference between the vena cava and the pulmonaryartery.

In some applications, the apparatus further includes:

a motor configured to drive the impeller to pump blood through thesubject's body, by rotating the impeller in a given direction ofrotation; and

a drive cable configured to extend from outside a body of the subject tothe axial shaft, the drive cable being configured to impart rotationalmotion from the motor to the impeller by rotating, at least a portion ofthe drive cable including a plurality of wires disposed in a coiledconfiguration that is such that, in response to the drive cable rotatingin the given direction of rotation, the plurality of wires disposed inthe coiled configuration at least partially unwind, such that theportion of the drive cable shortens axially.

In some applications, the impeller is coupled to the axial shaft suchthat the impeller causes the axial shaft to undergo axial back-and-forthmotion with respect to the proximal and distal bearings of the frame. Insome applications, the axial shaft is configured to clean interfacesbetween the axial shaft and the proximal and distal bearings of theframe, by undergoing the axial back-and-forth motion with respect to theproximal and distal bearings of the frame. In some applications, theaxial shaft is configured to reduce a build-up of heat at interfacesbetween the axial shaft and the proximal and distal bearings of theframe, by undergoing the axial back-and-forth motion with respect to theproximal and distal bearings of the frame, relative to if the axialshaft did not undergo the axial back-and-forth motion with respect tothe proximal and distal bearings of the frame.

There is further provided, in accordance with some applications of thepresent invention, apparatus including:

a blood pump including:

-   -   an impeller configured to be placed inside a body of a subject,        and configured to pump blood through the subject's body;    -   a frame configured to be disposed around the impeller,    -   the blood pump not including any thrust bearing configured to be        disposed within the subject's body.

In some applications, the blood pump further includes one or more thrustbearings configured to be disposed outside the subject's body, andopposition to thrust generated by the rotation of the impeller isprovided solely by the one or more thrust bearings disposed outside thesubject's body.

In some applications, the apparatus further includes:

a sensor configured to detect an indication of axial motion of theimpeller, and to generate a sensor signal in response thereto; and

a computer processor configured to receive the sensor signal and togenerate an output in response thereto.

In some applications, the computer processor is configured to generatean output indicating a cardiac cycle of the subject, in response toreceiving the sensor signal. In some applications, the computerprocessor is configured to determine left-ventricular pressure of thesubject, at least partially based upon the sensor signal. In someapplications, the computer processor is configured to change a rate ofrotation of the impeller, at least partially based upon the sensorsignal.

In some applications, the computer processor is configured:

to determine left-ventricular pressure of the subject, at leastpartially based upon the sensor signal, and

to change a rate of rotation of the impeller, at least partially basedupon the determined left-ventricular pressure.

In some applications, the computer processor is configured to reduce therate of rotation of the impeller, in response to determining that thesubject's left-ventricular pressure has decreased.

In some applications, the apparatus further includes:

a magnet, the impeller being coupled to the magnet such that axialmotion of the impeller causes the magnet to undergo axial motion;

a sensor configured to detect magnetic flux generated by the magnet, andto generate a sensor signal in response thereto; and

a computer processor configured to receive the sensor signal and togenerate an output in response thereto.

In some applications, the computer processor is configured to generatean output indicating a cardiac cycle of the subject, in response toreceiving the sensor signal. In some applications, the computerprocessor is configured to determine left-ventricular pressure of thesubject, at least partially based upon the sensor signal. In someapplications, the computer processor is configured to change a rate ofrotation of the impeller, at least partially based upon the sensorsignal.

In some applications, the computer processor is configured:

to determine left-ventricular pressure of the subject, at leastpartially based upon the sensor signal, and

to change a rate of rotation of the impeller, at least partially basedupon the determined left-ventricular pressure.

In some applications, the computer processor is configured to reduce therate of rotation of the impeller, in response to determining that thesubject's left-ventricular pressure has decreased.

In some applications, the impeller is configured to pump blood from afirst location within the subject's body to a second location within thesubject's body, and the impeller is configured to undergo axialback-and-forth motion with respect to the frame, in response to cyclicalchanges in a pressure difference between the first location and thesecond location. In some applications, the impeller is configured topump blood from a left ventricle of the subject to an aorta of thesubject, and the impeller is configured to undergo axial back-and-forthmotion with respect to the frame, in response to cyclical changes in apressure difference between the left ventricle and the aorta. In someapplications, the impeller is configured to pump blood from a rightventricle of the subject to a pulmonary artery of the subject, and theimpeller is configured to undergo axial back-and-forth motion withrespect to the frame, in response to cyclical changes in a pressuredifference between the right ventricle and the pulmonary artery. In someapplications, the impeller is configured to pump blood from a rightatrium of the subject to a right ventricle of the subject, and theimpeller is configured to undergo axial back-and-forth motion withrespect to the frame, in response to cyclical changes in a pressuredifference between the right atrium and the right ventricle. In someapplications, the impeller is configured to pump blood from a vena cavaof the subject to a right ventricle of the subject, and the impeller isconfigured to undergo axial back-and-forth motion with respect to theframe, in response to cyclical changes in a pressure difference betweenthe vena cava and the right ventricle. In some applications, theimpeller is configured to pump blood from a right atrium of the subjectto a pulmonary artery of the subject, and the impeller is configured toundergo axial back-and-forth motion with respect to the frame, inresponse to cyclical changes in a pressure difference between the rightatrium and the pulmonary artery. In some applications, the impeller isconfigured to pump blood from a vena cava of the subject to a pulmonaryartery of the subject, and the impeller is configured to undergo axialback-and-forth motion with respect to the frame, in response to cyclicalchanges in a pressure difference between the vena cava and the pulmonaryartery.

In some applications, the apparatus further includes:

a motor configured to drive the impeller to pump blood through thesubject's body, by rotating the impeller in a given direction ofrotation;

an axial shaft, the impeller being coupled to the axial shaft; and

a drive cable configured to extend from outside a body of the subject tothe axial shaft, the drive cable being configured to impart rotationalmotion from the motor to the impeller by rotating, at least a portion ofthe drive cable including a plurality of wires disposed in a coiledconfiguration that is such that, in response to the drive cable rotatingin the given direction of rotation, the plurality of wires disposed inthe coiled configuration at least partially unwind, such that theportion of the drive cable shortens axially.

In some applications:

the impeller includes proximal and distal bushings;

the frame includes proximal and distal bearings;

the apparatus further includes an axial shaft that:

-   -   passes through the proximal and distal bearings defined by the        frame and the proximal and distal bushings of the impeller,    -   is coupled to at least one of the proximal and distal bushings        of the impeller, such that the at least one bushing is held in        an axially-fixed position with respect to the axial shaft,    -   is not held in an axially-fixed position with respect to the        proximal and distal bearings,    -   such that the impeller causes the axial shaft to undergo axial        back-and-forth motion with respect to the proximal and distal        bearings of the frame.

In some applications, the axial shaft is configured to clean interfacesbetween the axial shaft and the proximal and distal bearings of theframe, by undergoing the axial back-and-forth motion with respect to theproximal and distal bearings of the frame. In some applications, theaxial shaft is configured to reduce a build-up of heat at interfacesbetween the axial shaft and the proximal and distal bearings of theframe, by undergoing the axial back-and-forth motion with respect to theproximal and distal bearings of the frame, relative to if the axialshaft did not undergo the axial back-and-forth motion with respect tothe proximal and distal bearings of the frame.

There is further provided, in accordance with some applications of thepresent invention, the following inventive concepts:

Inventive concept 1. Apparatus comprising:

an impeller comprising:

-   -   at least one helical elongate element;    -   a spring that is disposed inside of the helical elongate        element, and along an axis around which the helical elongate        element winds;    -   a film of material supported between the helical elongate        element and the spring; and    -   at least one flexible elongate element extending from the spring        to the helical elongate element and configured to maintain the        helical elongate element within a given distance from the        spring, the at least one flexible elongate element being        selected from the group consisting of: a string and a wire.        Inventive concept 2. The apparatus according to inventive        concept 1, wherein the impeller is configured such that in a        non-radially-constrained configuration of the impeller, an outer        diameter of the impeller at a location at which the outer        diameter is at its maximum is less than 8 mm.        Inventive concept 3. The apparatus according to inventive        concept 1, wherein the at least one helical elongate element        comprises a plurality of helical elongate elements, and wherein        the at least one flexible elongate element extends from the        spring to each of the helical elongate elements.        Inventive concept 4. The apparatus according to any one of        inventive concepts 1-3, wherein the impeller is configured to        pump blood through a body of a subject.        Inventive concept 5. The apparatus according to inventive        concept 4, wherein the impeller is configured to be placed in a        blood vessel of the subject.        Inventive concept 6. The apparatus according to inventive        concept 4, wherein the impeller is configured to be placed in a        cardiac chamber of the subject.        Inventive concept 7. The apparatus according to inventive        concept 4, wherein the impeller is configured to pump blood from        a left ventricle of a subject to an aorta of the subject.        Inventive concept 8. The apparatus according to inventive        concept 4, wherein the impeller is configured to pump blood from        a right ventricle of a subject to a pulmonary artery of the        subject.        Inventive concept 9. A method comprising:

placing into a body of a subject an impeller that includes:

-   -   at least one helical elongate element;    -   a spring that is disposed inside of the helical elongate        element, and along an axis around which the helical elongate        element winds;    -   a film of material supported between the helical elongate        element and the spring; and    -   at least one flexible elongate element extending from the spring        to the helical elongate element selected from the group        consisting of: a string and a wire; and

pumping blood through the subject's body by rotating the impeller, theflexible elongate element maintaining the helical elongate elementwithin a given distance from the spring, during the rotation of theimpeller.

Inventive concept 10. Apparatus comprising:

a blood pump comprising:

-   -   an impeller configured to be placed inside a cardiac chamber of        a subject;    -   a frame configured to be disposed around the impeller; and    -   a motor configured to drive the impeller to pump blood from the        cardiac chamber to a blood vessel of the subject, by rotating        the impeller,    -   the impeller being configured to undergo axial motion with        respect to the frame, in response to cyclical changes in a        pressure difference between the cardiac chamber and the blood        vessel.        Inventive concept 11. A method comprising:

placing an impeller of a blood pump inside a cardiac chamber of asubject, with a frame disposed around the impeller; and

driving the impeller to pump blood from the cardiac chamber to a bloodvessel of the subject, by rotating the impeller,

placement of the impeller inside the cardiac chamber being such that theimpeller is allowed to undergo axial motion with respect to the frame,in response to cyclical changes in a pressure difference between thecardiac chamber and the blood vessel.

Inventive concept 12. Apparatus comprising:

a blood pump comprising:

-   -   an impeller configured to be placed inside a first blood vessel        of a subject;    -   a frame configured to be disposed around the impeller; and    -   a motor configured to drive the impeller to pump blood from the        first blood vessel to a second blood vessel of the subject, by        rotating the impeller,

the impeller being configured to undergo axial motion with respect tothe frame, in response to cyclical changes in a pressure differencebetween the first blood vessel and the second blood vessel.

Inventive concept 13. A method comprising:

placing an impeller of a blood pump inside a first blood vessel of asubject, with a frame disposed around the impeller; and

driving the impeller to pump blood from the first blood vessel to asecond blood vessel of the subject, by rotating the impeller,

placement of the impeller inside the first blood vessel being such thatthe impeller is allowed to undergo axial motion with respect to theframe, in response to cyclical changes in a pressure difference betweenthe cardiac chamber and the blood vessel.

Inventive concept 14. Apparatus comprising:

a blood pump comprising:

-   -   an impeller configured to be placed inside a body of a subject,        and configured to rotate such as to pump blood through the        subject's body;    -   a frame configured to be disposed around the impeller; and    -   one or more thrust bearings configured to be disposed outside        the subject's body, wherein opposition to thrust generated by        the rotation of the impeller is provided solely by the one or        more thrust bearings disposed outside the subject's body.        Inventive concept 15. A method comprising:

placing an impeller of a blood pump inside a body of a subject, with aframe disposed around the impeller; and

driving the impeller to pump blood through the subject's body, byrotating the impeller, opposition to thrust generated by the rotation ofthe impeller being provided solely by one or more thrust bearingsdisposed outside the subject's body.

Inventive concept 16. Apparatus comprising:

a blood-pump tube;

a blood pump configured to be disposed within the blood-pump tube, andto pump blood through the blood-pump tube;

at least one blood-pressure-measurement tube that defines an opening ata distal end thereof, and that is configured to extend to at least anouter surface of the blood-pump tube, such that the opening at thedistal end of the blood-pressure-measurement tube is in direct fluidcommunication with a bloodstream of the subject outside the blood-pumptube; and

at least one pressure sensor configured to measure pressure of thebloodstream of the subject outside the blood-pump tube by measuringpressure of blood within the blood-pressure-measurement tube.

Inventive concept 17. The apparatus according to inventive concept 16,wherein the blood pump comprises an impeller that is configured to pumpblood through the blood-pump tube, by rotating.

Inventive concept 18. The apparatus according to inventive concept 16,wherein the blood-pressure-measurement tube is configured to pass alongan outer surface of the blood-pump tube from the proximal end of theblood-pump tube until the opening at the distal end of theblood-pressure-measurement tube.Inventive concept 19. The apparatus according to inventive concept 16,further comprising at least one computer processor that is configured toreceive an indication of the blood pressure measured within theblood-pressure-measurement tube and to control the pumping of blood bythe blood pump in response to the blood pressure measured within theblood-pump tube.Inventive concept 20. The apparatus according to any one of inventiveconcepts 16-19, wherein the at least one blood-pressure measurement tubecomprises at least one left-ventricular blood-pressure measurement tubethat is configured to extend to the outer surface of the blood-pump tubeat a location along the tube that is configured to be within thesubject's left ventricle proximal to the blood pump, and wherein thepressure sensor is configured to measure left-ventricular pressure ofthe subject by measuring pressure of blood within the left-ventricularblood-pressure-measurement tube.Inventive concept 21. The apparatus according to inventive concept 20,wherein the at least one blood-pressure measurement tube comprises twoor more left-ventricular blood-pressure measurement tubes that areconfigured to extend to the outer surface of the blood-pump tube atlocations along the blood-pump tube that are configured to be within thesubject's left ventricle proximal to the blood pump, and wherein the atleast one pressure sensor is configured to measure left-ventricularpressure of the subject by measuring pressure of blood within at leastone of the left-ventricular blood-pressure-measurement tubes.Inventive concept 22. The apparatus according to inventive concept 21,

wherein the at least one pressure sensor is configured to measurepressure of blood within each of the two or more left-ventricularblood-pressure-measurement tubes,

the apparatus further comprising at least one computer processor that isconfigured:

-   -   to receive an indication of the blood pressure measured within        each of the two or more left-ventricular        blood-pressure-measurement tubes,    -   in response thereto, to determine that the opening of one of the        two or more left-ventricular blood-pressure-measurement tubes is        occluded, and    -   in response thereto, to determine left-ventricular pressure of        the subject, based upon the blood pressure measured within a        different one of the two or more left-ventricular        blood-pressure-measurement tubes.        Inventive concept 23. The apparatus according to inventive        concept 20, wherein the at least one blood-pressure measurement        tube further comprises at least one aortic blood-pressure        measurement tube that is configured to extend to the outer        surface of the blood-pump tube at a location along the        blood-pump tube that is configured to be within the subject's        aorta, and wherein the pressure sensor is configured to measure        aortic pressure of the subject by measuring pressure of blood        within the aortic blood-pressure-measurement tube.        Inventive concept 24. The apparatus according to inventive        concept 23, wherein the at least one aortic blood-pressure        measurement tube comprises two or more aortic blood-pressure        measurement tubes that are configured to extend to the outer        surface of the blood-pump tube at locations along the blood-pump        tube that are configured to be within the subject's aorta, and        wherein the at least one pressure sensor is configured to        measure aortic pressure of the subject by measuring pressure of        blood within at least one of the aortic        blood-pressure-measurement tubes.        Inventive concept 25. The apparatus according to any one of        inventive concepts 16-19, wherein the at least one        blood-pressure measurement tube comprises at least one aortic        blood-pressure measurement tube that is configured to extend to        the outer surface of the blood-pump tube at a location along the        blood-pump tube that is configured to be within the subject's        aorta, and wherein the pressure sensor is configured to measure        aortic pressure of the subject by measuring pressure of blood        within the aortic blood-pressure-measurement tube.        Inventive concept 26. The apparatus according to inventive        concept 25, wherein the at least one aortic blood-pressure        measurement tube comprises two or more aortic blood-pressure        measurement tubes that are configured to extend to the outer        surface of the blood-pump tube at locations along the blood-pump        tube that are configured to be within the subject's aorta, and        wherein the at least one pressure sensor is configured to        measure aortic pressure of the subject by measuring pressure of        blood within at least one of the aortic        blood-pressure-measurement tubes.        Inventive concept 27. The apparatus according to inventive        concept 26,

wherein the at least one pressure sensor is configured to measurepressure of blood within each of the two or more aorticblood-pressure-measurement tubes,

the apparatus further comprising at least one computer processor that isconfigured:

-   -   to receive an indication of the blood pressure measured within        each of the two or more aortic blood-pressure-measurement tubes,    -   in response thereto, to determine that the opening of one of the        two or more aortic blood-pressure-measurement tubes is occluded,        and    -   in response thereto, to determine aortic pressure of the        subject, based upon the blood pressure measured within a        different one of the two or more aortic        blood-pressure-measurement tubes.        Inventive concept 28. The apparatus according to any one of        inventive concepts 16-19, wherein the blood-pressure-measurement        tube is configured to extend from outside a body of the subject        to the opening at the distal end, and wherein the at least one        pressure sensor is configured to be disposed outside the        subject's body.        Inventive concept 29. The apparatus according to inventive        concept 28, wherein the blood pump comprises an impeller        disposed upon an axial shaft, the impeller being configured to        pump blood from the left ventricle to the aorta by rotating,        wherein the apparatus further comprises:

a motor disposed outside the subject's body, and configured to drive theimpeller to rotate;

a drive cable extending from outside the subject's body to the axialshaft, and configured to impart rotational motion from the motor to theimpeller, by rotating; and

an outer tube configured to extend from outside the subject's body towithin the blood-pump tube,

-   -   wherein the drive cable and the blood-pressure-measurement tube        are configured to be disposed within the outer tube.        Inventive concept 30. The apparatus according to inventive        concept 29,

wherein the at least one blood-pressure measurement tube comprises atleast one left-ventricular blood-pressure measurement tube that isconfigured to extend to the outer surface of the blood-pump tube at alocation along the blood-pump tube that is configured to be within thesubject's left ventricle proximal to the blood pump, and wherein the atleast one pressure sensor is configured to measure left-ventricularpressure of the subject by measuring pressure of blood within theleft-ventricular blood-pressure-measurement tube;

the apparatus further comprising an aortic blood-pressure-measurementtube that defines an opening at a distal end thereof, and that isconfigured to extend from outside the subject's body to an outer surfaceof the outer tube within an aorta of the subject, such that the openingat the distal end of the blood-pressure-measurement tube is in directfluid communication with an aortic bloodstream of the subject;

wherein the at least one pressure sensor is further configured tomeasure aortic pressure of the subject by measuring pressure of bloodwithin the aortic blood-pressure-measurement tube.

Inventive concept 31. The apparatus according to inventive concept 29,

wherein the at least one blood-pressure measurement tube comprises atleast one left-ventricular blood-pressure measurement tube that isconfigured to extend to the outer surface of the blood-pump tube at alocation along the blood-pump tube that is configured to be within thesubject's left ventricle proximal to the blood pump, and wherein the atleast one pressure sensor is configured to measure left-ventricularpressure of the subject by measuring pressure of blood within theleft-ventricular blood-pressure-measurement tube;

the apparatus further comprising an aortic blood-pressure-measurementtube that defines an opening at a distal end thereof, and that isconfigured to extend from outside the subject's body to a portion of anouter surface of the outer tube that is disposed within the blood-pumptube, such that the opening at the distal end of theblood-pressure-measurement tube is in direct fluid communication with anaortic bloodstream of the subject;

wherein the at least one pressure sensor is further configured tomeasure aortic pressure of the subject by measuring pressure of bloodwithin the aortic blood-pressure-measurement tube.

Inventive concept 32. The apparatus according to inventive concept 29,wherein the outer tube defines a groove in a portion of an outer surfaceof the outer tube that is configured to be disposed within theblood-pump tube, and wherein, during insertion of the ventricular assistdevice into the subject's body, a portion of theblood-pressure-measurement tube that is configured to extend from withinthe blood-pump tube to the outer surface of the blood-pump tube isconfigured to be disposed within the groove, such that the portion ofthe blood-pressure-measurement tube does not protrude from the outersurface of the outer tube.Inventive concept 33. The apparatus according to inventive concept 28,wherein a diameter of the blood-pressure-measurement tube at leastwithin a distal portion of the blood-pressure-measurement tube is lessthan 0.5 mm.Inventive concept 34. The apparatus according to inventive concept 33,wherein the diameter of the blood-pressure-measurement tube at leastwithin the distal portion of the blood-pressure-measurement tube is morethan 0.2 mm.Inventive concept 35. A method comprising:

placing into a body of a subject:

-   -   a blood-pump tube,    -   a blood pump disposed within the blood-pump tube, and    -   at least one blood-pressure-measurement tube that defines an        opening at a distal end thereof, and that extends to at least an        outer surface of the blood-pump tube, such that the opening at        the distal end of the blood-pressure-measurement tube is in        direct fluid communication with a bloodstream of the subject        outside the blood-pump tube;

pumping blood through the blood-pump tube, using the blood pump; and

measuring pressure of the bloodstream of the subject outside theblood-pump tube by measuring pressure of blood within theblood-pressure-measurement tube.

Inventive concept 36. Apparatus comprising:

a blood pump comprising:

-   -   a tube;    -   an impeller configured to be disposed within the tube and        configured to rotate, such as to pump blood through the tube;    -   a frame disposed around the impeller; and    -   a stator configured to reduce rotational flow components from        blood flow generated by rotation of the impeller, the stator        comprising:        -   a plurality of struts that are integral with the frame and            that are curved; and        -   a flexible material coupled to the curved struts such as to            form a plurality of curved projections.            Inventive concept 37. The apparatus according to inventive            concept 36, wherein the curvature of the curved projections            opposes the direction of rotation of the impeller.            Inventive concept 38. The apparatus according to inventive            concept 36, wherein the curvature of the curved projections            is such that, from distal ends of the curved projections to            proximal ends of the curved projections, the curved            projections become progressively closer to being parallel            with a longitudinal axis of the frame.            Inventive concept 39. The apparatus according to inventive            concept 36, wherein the flexible material is shaped to            define a lumen therethrough.            Inventive concept 40. A method comprising:

placing a blood pump into a subject's body, the blood pump including:

-   -   a tube,    -   an impeller configured to be disposed within the tube,    -   a frame disposed around the impeller, and    -   a stator that includes a plurality of struts that are integral        with the frame and that are curved, and a flexible material        coupled to the curved struts such as to form a plurality of        curved projections; and

pumping blood through the tube using the impeller, the stator reducingrotational flow components from blood flow generated by rotation of theimpeller.

Inventive concept 41. Apparatus comprising:

a ventricular assist device comprising:

-   -   an axial shaft;    -   an impeller disposed on the axial shaft and configured to be        placed in a left ventricle of a subject;    -   a motor configured to be disposed outside a body of the subject,        and configured to drive the impeller to pump blood from the left        ventricle to an aorta of the subject by rotating the impeller;    -   a drive cable configured to extend from outside the subject's        body to the axial shaft, the drive cable being configured to        impart rotational motion from the motor to the impeller by        rotating, the drive cable comprising a first portion configured        to be disposed at least partially within an aortic arch of the        subject, and a second portion configured to be disposed at least        partially within a descending aorta of the subject,    -   the first portion of the drive cable comprising a first number        of wires disposed in a coiled configuration, and the second        portion of the drive cable comprising a second number of wires        disposed in a coiled configuration, the first number being lower        than the second number.        Inventive concept 42. The apparatus according to inventive        concept 41, wherein a length of the first portion of the drive        cable is between 20 cm and 40 cm.        Inventive concept 43. The apparatus according to inventive        concept 41, wherein a length of the second portion of the drive        cable is between 60 cm and 100 cm.        Inventive concept 44. The apparatus according to inventive        concept 41, wherein the first portion of the drive cable        comprises between 4 and 8 wires disposed in the coiled        configuration, and the second portion of the drive cable        comprises between 8 and 12 wires disposed in the coiled        configuration.        Inventive concept 45. Apparatus comprising:

a blood pump comprising:

-   -   an axial shaft;    -   an impeller disposed on the axial shaft;    -   a motor configured to be disposed outside a body of the subject,        and configured to drive the impeller to pump blood through the        subject's body by rotating the impeller;    -   a drive cable configured to extend from outside the subject's        body to the axial shaft, the drive cable being configured to        impart rotational motion from the motor to the impeller by        rotating, the drive cable comprising a first portion configured        to be disposed at least partially within a curved portion of        vasculature of the subject, and a second portion configured to        be disposed at least partially within a straight portion of        vasculature of the subject,    -   the first portion of the drive cable comprising a first number        of wires disposed in a coiled configuration, and the second        portion of the drive cable comprising a second number of wires        disposed in a coiled configuration, the first number being lower        than the second number.        Inventive concept 46. Apparatus comprising:

a blood pump comprising:

-   -   an axial shaft;    -   an impeller disposed on the axial shaft;    -   a motor configured to be disposed outside a body of the subject,        and configured to drive the impeller to pump blood from a distal        end of the impeller to a proximal end of the impeller, by        rotating the impeller in a given direction of rotation;    -   a drive cable configured to extend from outside the subject's        body to the axial shaft, the drive cable being configured to        impart rotational motion from the motor to the impeller by        rotating,        -   at least a portion of the drive cable comprising a plurality            of wires disposed in a coiled configuration that is such            that, in response to the drive cable rotating in the given            direction of rotation, the plurality of wires disposed in            the coiled configuration at least partially unwind, such            that the portion of the drive cable shortens axially.            Inventive concept 47. The apparatus according to inventive            concept 46, wherein the impeller is configured to pump blood            from a first location to a second location, and wherein the            impeller is configured to undergo axial back-and-forth            motion, in response to cyclical changes in a pressure            difference between the first location and the second            location.            Inventive concept 48. A method comprising:

placing a blood pump into a body of a subject, the blood pump including:

-   -   an axial shaft,    -   an impeller disposed on the axial shaft, and    -   a drive cable extending from outside the subject's body to the        axial shaft; and

driving the impeller to pump blood from a distal end of the impeller toa proximal end of the impeller by imparting rotational motion theimpeller via the drive cable, at least a portion of the drive cablecomprising a plurality of wires disposed in a coiled configuration thatis such that, in response to the drive cable rotating in the givendirection of rotation, the plurality of wires disposed in the coiledconfiguration at least partially unwind, such that the portion of thedrive cable shortens axially.

Inventive concept 49. Apparatus comprising:

a blood pump comprising:

-   -   an axial shaft;    -   an impeller disposed on the axial shaft;    -   a motor configured to be disposed outside a body of the subject,        and configured to drive the impeller to pump blood in a proximal        direction by rotating the impeller in a given direction of        rotation;    -   a drive cable configured to extend a proximal end of the drive        cable disposed outside the subject's body to a distal end of the        drive cable, which is coupled to the axial shaft, the drive        cable being configured to impart rotational motion from the        motor to the impeller by rotating;    -   an outer tube disposed around the drive cable; and    -   fluid disposed between the outer tube and the drive cable,    -   at least a portion of the drive cable comprising a plurality of        wires disposed in a coiled configuration that is such that in        response to the drive cable rotating in the given direction of        rotation, the plurality of wires are configured to pump the        fluid toward the proximal end of the drive cable.        Inventive concept 50. A method comprising:

placing a blood pump into a body of a subject, the blood pump including:

-   -   an axial shaft,    -   an impeller disposed on the axial shaft,    -   a drive cable extending from outside the subject's body to the        axial shaft,    -   an outer tube disposed around the drive cable, and    -   a fluid disposed between the drive cable and the outer tube; and

driving the impeller to pump blood from a distal end of the impeller toa proximal end of the impeller by imparting rotational motion theimpeller via the drive cable, at least a portion of the drive cablecomprising a plurality of wires disposed in a coiled configuration thatis such that, in response to the drive cable rotating in the givendirection of rotation, the plurality of wires are configured to pump thefluid toward the proximal end of the drive cable.

Inventive concept 51. Apparatus comprising:

a blood pump comprising:

-   -   an impeller;    -   a motor configured to drive the impeller to pump blood by        rotating the impeller, the impeller being configured to undergo        axial motion, in response to changes in a pressure difference        against which the impeller is pumping the blood;    -   a magnet, the impeller being coupled to the magnet such that        axial motion of the impeller causes the magnet to undergo axial        motion;    -   a sensor configured to detect magnetic flux generated by the        magnet, and to generate a sensor signal in response thereto; and    -   a computer processor configured to receive the sensor signal and        to generate an output in response thereto.        Inventive concept 52. The apparatus according to inventive        concept 51, wherein the computer processor is configured to        generate an output indicating a cardiac cycle of the subject, in        response to receiving the sensor signal.        Inventive concept 53. The apparatus according to inventive        concept 51, wherein the computer processor is configured to        determine left-ventricular pressure of the subject, at least        partially based upon the sensor signal.        Inventive concept 54. The apparatus according to any one of        inventive concepts 51-53, wherein the computer processor is        configured to change a rate of rotation of the impeller, at        least partially based upon the sensor signal.        Inventive concept 55. The apparatus according to inventive        concept 54, wherein the computer processor is configured:

to determine left-ventricular pressure of the subject, at leastpartially based upon the sensor signal, and

to change a rate of rotation of the impeller, at least partially basedupon the determined left-ventricular pressure.

Inventive concept 56. The apparatus according to inventive concept 55,wherein the computer processor is configured to reduce the rate ofrotation of the impeller, in response to determining that the subject'sleft-ventricular pressure has decreased.

Inventive concept 57. Apparatus comprising:

a blood pump comprising:

-   -   an impeller;    -   a motor configured to drive the impeller to pump blood by        rotating the impeller, the impeller being configured to undergo        axial motion, in response to changes in a pressure difference        against which the impeller is pumping the blood;    -   a sensor configured to detect an indication of the axial motion        of the impeller, and to generate a sensor signal in response        thereto; and    -   a computer processor configured to receive the sensor signal and        to generate an output in response thereto.        Inventive concept 58. A method comprising:

placing a blood pump inside a body of a subject, the blood pumpincluding an impeller;

driving the impeller to pump blood by rotating the impeller, theimpeller being configured to undergo axial motion, in response tochanges in a pressure difference against which the impeller is pumpingthe blood;

detecting an indication of the axial motion of the impeller, andgenerating a sensor signal in response thereto; and

receiving the sensor signal, and generating an output in responsethereto.

Inventive concept 59. Apparatus comprising:

a blood pump comprising:

-   -   an impeller;    -   a frame,        -   the impeller and the frame being configured to be inserted            into a body of a subject, such that, within the subject's            body, the frame is disposed around the impeller; and

a computer processor configured to drive a motor unit to,simultaneously, (a) drive the impeller to pump blood through thesubject's body, by driving the impeller to rotate, and (b) drive theimpeller to move axially within the frame in a back-and-forth motion.

Inventive concept 60. A method comprising:

placing, into a body of a subject, a blood pump that includes animpeller and a frame, such that the frame is disposed around theimpeller; and

simultaneously:

-   -   driving the impeller to pump blood through the subject's body,        by driving the impeller to rotate; and    -   driving the impeller to move axially within the frame in a        back-and-forth motion.        Inventive concept 61. Apparatus comprising:

a blood pump comprising:

-   -   an axial shaft;    -   an impeller disposed on the axial shaft and configured to be        placed in a left ventricle of a subject;    -   a motor configured to be disposed outside a body of the subject,        and configured to drive the impeller to rotate;    -   a drive cable configured to extend from outside of the subject's        body to the axial shaft, via an aortic arch of the subject, the        drive cable being configured to impart rotational motion from        the motor to the impeller, by rotating;    -   a tube, within which the drive cable is configured to be        disposed during rotation of the drive cable, the tube being        configured to remain stationary during rotation of the drive        cable; and    -   a plurality of ball bearings configured to be disposed between        the drive cable and the tube, such as to reduce friction between        the drive cable and the tube during movement of the drive cable        with respect to the tube.        Inventive concept 62. The apparatus according to inventive        concept 61, wherein the ball bearings are configured to be        disposed between the drive cable and the tube, at least at        portions of the drive cable and the tube that are configured to        be disposed within the subject's aortic arch, during the        rotation of the impeller.        Inventive concept 63. Apparatus comprising:

a blood pump comprising:

-   -   an axial shaft;    -   an impeller disposed on the axial shaft and configured to be        placed inside a body of a subject;    -   a motor configured to be disposed outside the subject's body;    -   a drive cable configured to extend from outside the subject's        body to the axial shaft;    -   exactly two driving magnets disposed in a driving magnet        housing, which is coupled to the motor; and    -   a driven magnet coupled to the drive cable and disposed between        the driving magnets such there is axial overlap between the        driving magnets and the driven magnets, the driven magnet        defining a single North pole and a single South pole that are        divided along an axial length of the driven magnet, the motor        being configured to impart rotational motion to the impeller by        rotating the drive cable by rotating the driven magnet, by        rotating the driving magnet housing.        Inventive concept 64. A method comprising:

placing, into a subject's body, a blood pump that includes:

-   -   an axial shaft,    -   an impeller disposed on the axial shaft, and    -   a drive cable extending from outside the subject's body to the        axial shaft; and driving the impeller to rotate by:    -   using a motor to rotate exactly two driving magnets disposed in        a driving magnet housing, which is coupled to the motor,    -   the driving magnets being configured to thereby drive a driven        magnet to rotate, the driven magnet being coupled to the drive        cable and disposed between the driving magnets such there is        axial overlap between the driving magnets and the driven        magnets, the driven magnet defining a single North pole and a        single South pole that are divided along an axial length of the        driven magnet.        Inventive concept 65. Apparatus comprising:

a blood pump comprising:

-   -   an axial shaft;    -   an impeller disposed on the axial shaft and configured to be        placed inside a body of a subject;    -   a motor configured to be disposed outside the subject's body;    -   a drive cable configured to extend from outside the subject's        body to the axial shaft;    -   exactly two driven magnets disposed in a driven magnet housing,        which is coupled to the drive cable; and    -   a drive magnet coupled to the motor and disposed between the        driven magnets such there is axial overlap between the driven        magnets and the driving magnet, the driving magnet defining a        single North pole and a single South pole that are divided along        an axial length of the driving magnet, the motor being        configured to impart rotational motion to the impeller by        rotating the drive cable, by rotating the driven magnets, by        rotating the driving magnet.        Inventive concept 66. A method comprising:

placing, into a subject's body, a blood pump that includes:

-   -   an axial shaft,    -   an impeller disposed on the axial shaft, and    -   a drive cable extending from outside the subject's body to the        axial shaft; and driving the impeller to rotate by:    -   using a motor to rotate a drive magnet coupled to the motor, the        drive magnet defining a single North pole and a single South        pole that are divided along an axial length of the driving        magnet,    -   the driving magnet being configured to thereby drive driven        magnets to rotate, the driven magnets comprising exactly two        driven magnets disposed in a driven magnet housing, the driven        magnet housing being coupled to the drive cable and being        disposed around the drive magnet.        Inventive concept 67. Apparatus comprising:

a blood pump comprising:

-   -   an axial shaft;    -   an impeller disposed on the axial shaft and configured to be        placed inside a body of a subject;    -   a motor configured to be disposed outside the subject's body,        and configured to drive the impeller to pump blood by rotating        the impeller in a given direction of rotation;    -   a drive cable configured to extend from outside the subject's        body to the axial shaft, the drive cable being configured to        impart rotational motion from the motor to the impeller by        rotating, and the drive cable comprising a plurality of wires        that are disposed in a coiled configuration and that are coupled        to the axial shaft,    -   the axial shaft defining grooves at an interface between the        drive cable and the axial shaft, the grooves being configured        such that stress generated by the wires at the interface is        spread over radii of the grooves.        Inventive concept 68. Apparatus comprising:

a blood pump comprising:

-   -   an axial shaft;    -   an impeller disposed on the axial shaft and configured to be        placed inside a body of a subject;    -   a motor configured to be disposed outside the subject's body,        and configured to drive the impeller to pump blood by rotating        the impeller in a given direction of rotation;    -   a drive cable configured to extend from outside the subject's        body to the axial shaft, the drive cable being configured to        impart rotational motion from the motor to the impeller by        rotating, and the drive cable comprising a plurality of wires        that are disposed in a coiled configuration and that are coupled        to the axial shaft,    -   the coiled wires being shaped such that as the coiled wires        approach an interface between the drive cable and the axial        shaft, a pitch of the wires is increased, such that stress at        locations at which the wires of the drive cable are coupled to        the axial shaft is reduced, relative to if the pitch of the        wires were not increased.        Inventive concept 69. Apparatus comprising:

a blood pump comprising:

-   -   an axial shaft;    -   an impeller disposed on the axial shaft and configured to be        placed inside a body of a subject;    -   a motor configured to be disposed outside the subject's body,        and configured to drive the impeller to pump blood by rotating        the impeller in a given direction of rotation;    -   a drive cable configured to extend from outside the subject's        body to the axial shaft, the drive cable being configured to        impart rotational motion from the motor to the impeller by        rotating,    -   the drive cable comprising first and second portions, the first        portion of the drive cable comprising a first number of wires        disposed in a coiled configuration, and the second portion of        the drive cable comprising a second number of wires disposed in        a coiled configuration, the first number being lower than the        second number; and    -   an interface component, the first and second portions of the        drive cable being coupled to each other via the interface        component,    -   the interface component defining grooves at an interface between        at least one of the drive cable portions and the interface        component, the grooves being configured such that stress        generated by the wires at the interface is spread over radii of        the grooves.        Inventive concept 70. Apparatus comprising:

a blood pump comprising:

-   -   an axial shaft;    -   an impeller disposed on the axial shaft and configured to be        placed inside a body of a subject;    -   a motor configured to be disposed outside the subject's body,        and configured to drive the impeller to pump blood by rotating        the impeller in a given direction of rotation;    -   a drive cable configured to extend from outside the subject's        body to the axial shaft, the drive cable being configured to        impart rotational motion from the motor to the impeller by        rotating,    -   the drive cable comprising first and second portions, the first        portion of the drive cable comprising a first number of wires        disposed in a coiled configuration, and the second portion of        the drive cable comprising a second number of wires disposed in        a coiled configuration, the first number being lower than the        second number; and    -   an interface component, the first and second portions of the        drive cable being coupled to each other via the interface        component,    -   the coiled wires of at least one of the portions of the drive        cable being shaped such that, as the coiled wires approach the        interface component, a pitch of the wires is increased, such        that stress at locations at which the wires are coupled to the        interface component is reduced relative to if the pitch of the        wires were not increased.        Inventive concept 71. Apparatus comprising:

a ventricular assist device comprising:

-   -   a tube configured to traverse an aortic valve of a subject, such        that a proximal portion of the tube is disposed within an aorta        of the subject and a distal portion of the tube is disposed        within a left ventricle of the subject, the tube defining one or        more blood inlet openings within the distal portion of the tube,        and one or more blood outlet openings within the proximal        portion of the tube;    -   a blood pump configured to be disposed within the tube, and to        pump blood from the left ventricle into the tube through the one        or more blood inlet openings, and out of the tube into the aorta        through the one or more blood outlet openings; and    -   a radially-expandable atraumatic distal tip portion configured        to be disposed within the subject's left ventricle distally with        respect to the one or more blood inlet openings, the distal tip        portion being configured to be inserted into the left ventricle        in a radially-constrained configuration, and to assume a        non-radially-constrained configuration within the subject's left        ventricle in which at least a radially-expandable portion of the        distal tip portion is radially expanded relative to the        radially-constrained configuration of the distal tip portion.        Inventive concept 72. The apparatus according to inventive        concept 71, wherein the distal tip portion comprises a braided        shape-memory alloy that is at least partially covered with a        blood impermeable material.        Inventive concept 73. The apparatus according to inventive        concept 71, wherein the distal tip portion is configured such        that, in the non-radially-constrained configuration of the        distal tip portion, the radially-expandable portion of the        distal tip portion separates the one or more blood inlet        openings from an interventricular septum within the left        ventricle.        Inventive concept 74. The apparatus according to inventive        concept 71, wherein the distal tip portion is configured such        that, in the non-radially-constrained configuration of the        distal tip portion, the radially-expandable portion of the        distal tip portion separates the one or more blood inlet        openings from chordae tendineae within the left ventricle.        Inventive concept 75. The apparatus according to inventive        concept 71, wherein the distal tip portion is configured such        that, in the non-radially-constrained configuration of the        distal tip portion, the radially-expandable portion of the        distal tip portion separates the one or more blood inlet        openings from papillary muscles within the left ventricle.        Inventive concept 76. The apparatus according to inventive        concept 71, wherein the distal tip portion is configured such        that, in the non-radially-constrained configuration of the        distal tip portion, the radially-expandable portion of the        distal tip portion separates the one or more blood inlet        openings from an apex of the left ventricle.        Inventive concept 77. The apparatus according to inventive        concept 71, wherein the distal tip portion is configured such        that, in the non-radially-constrained configuration of the        distal tip portion, the radially-expandable portion of the        distal tip portion separates the one or more blood inlet        openings from inner structures of the left ventricle in three        dimensions.        Inventive concept 78. The apparatus according to inventive        concept 71, wherein the distal tip portion is configured such        that, in the non-radially-constrained configuration of the        distal tip portion, the radially-expandable portion of the        distal tip portion directs blood flow from the left ventricle        into the one or more blood inlet openings.        Inventive concept 79. The apparatus according to any one of        inventive concepts 71-78, wherein:

in the radially-constrained configuration of the distal tip portion, adistal region of the distal tip portion is configured to be leastsemi-rigid, and is shaped to radially converge along a longitudinaldirection toward a distal end of the distal tip portion;

the ventricular assist device is configured to be inserted into thesubject's body via a puncture, in the subject's body, and

during the insertion of the ventricular assist device the distal regionof the distal tip portion is configured to act as a dilator by dilatingthe puncture.

Inventive concept 80. The apparatus according to any one of inventiveconcepts 71-78, wherein the distal tip portion is configured such thatin the non-radially-constrained configuration of the distal tip portion,a distal end of the distal tip portion is enveloped within theradially-expandable portion of the distal tip portion.Inventive concept 81. The apparatus according to inventive concept 80,wherein the distal tip portion is configured to prevent the distal endof the distal tip portion becoming entangled with chordae tendineae ofthe left ventricle by the distal end of the distal tip portion beingenveloped within the radially expanded portion of the distal tip.Inventive concept 82. The apparatus according to inventive concept 80,wherein the distal tip portion is configured to prevent the distal endof the distal tip portion causing trauma to an internal structure of theleft ventricle by the distal end of the distal tip portion beingenveloped within the radially-expandable portion of the distal tipportion.Inventive concept 83. The apparatus according to inventive concept 80,wherein the distal end of the distal tip portion is configured to beenveloped within the radially-expandable portion of the distal tipportion, by the distal end of the distal tip portion inverting.Inventive concept 84. The apparatus according to inventive concept 80,wherein the distal end of the distal tip portion is configured to beenveloped within the radially-expandable portion of the distal tipportion, by the distal end of the distal tip portion being retractedproximally, such that the distal end is disposed within theradially-expandable portion of the distal tip portion.Inventive concept 85. Apparatus comprising:

a ventricular assist device configured to be inserted into a subject'sbody via a puncture, the ventricular assist device comprising:

-   -   a tube configured to traverse an aortic valve of a subject, such        that a proximal portion of the tube is disposed within an aorta        of the subject and a distal portion of the tube is disposed        within a left ventricle of the subject, the tube defining one or        more blood inlet openings within the distal portion of the tube,        and one or more blood outlet openings within the proximal        portion of the tube;    -   a blood pump configured to be disposed within the tube, and to        pump blood from the left ventricle into the tube through the one        or more blood inlet openings, and out of the tube into the aorta        through the one or more blood outlet openings; and    -   a distal tip portion configured:        -   to have a radially-constrained configuration in which a            distal region of the distal tip portion is at least            partially rigid, and is shaped to radially converge along a            longitudinal direction toward a distal end of the distal tip            portion, the distal region being configured to act as a            dilator by dilating the puncture, during insertion of the            ventricular assist device into the subject's body, and        -   to have a non-radially-constrained configuration that the            distal tip region is configured to assume within the            subject's left ventricle in which the radially-expandable            portion of the distal tip portion is configured to be            atraumatic and to separate the one or more blood inlet            openings from internal structures of the subject's left            ventricle.            Inventive concept 86. A method comprising:

operating a blood pump, the blood pump including:

-   -   an axial shaft,    -   an impeller disposed on the axial shaft and disposed in a left        ventricle of a subject;    -   a motor disposed outside a body of the subject, and configured        to drive the impeller to rotate,    -   a drive cable extending from outside the subject's body to the        axial shaft via an aortic arch of the subject, and configured to        impart rotational motion from the motor to the impeller, by        rotating, and    -   a tube, within which the drive cable is disposed, the tube being        configured to remain stationary during rotation of the drive        cable; and

while operating the blood pump, pumping fluid into a space between thedrive cable and the tube, such that the fluid fills the space betweenthe drive cable and the tube, but without releasing the fluid into abloodstream of the subject.

Inventive concept 87. A method comprising:

operating a blood pump, the blood pump including:

-   -   an axial shaft,    -   an impeller disposed on the axial shaft and disposed in a left        ventricle of a subject,    -   a motor disposed outside a body of the subject, and configured        to drive the impeller to rotate,    -   a drive cable extending from outside the subject's body to the        axial shaft via an aortic arch of the subject, and configured to        impart rotational motion from the motor to the impeller, by        rotating, and    -   a tube, within which the drive cable is disposed, the tube being        configured to remain stationary during rotation of the drive        cable;

prior to operating the blood pump, pumping fluid into a space betweenthe drive cable and the tube, such that the fluid fills the spacebetween the drive cable and the tube, but without releasing the fluidinto a bloodstream of the subject; and

leaving the fluid within the space between the drive cable and the tube,during the operation of the blood pump.

Inventive concept 88. Apparatus comprising:

a left-ventricular assist device configured to assist left-ventricularfunctioning of a subject, the left ventricular assist device comprising:

-   -   a tube configured to traverse an aortic valve of the subject,        such that a proximal portion of the tube is at least partially        disposed within an ascending aorta of the subject and a distal        portion of the tube is disposed at least partially a left        ventricle of the subject;    -   a frame disposed within the distal portion of the tube, the        frame being configured to hold a distal portion of the tube in        an open state,    -   the frame not being disposed within the proximal portion of the        tube, and the proximal portion of the tube thereby being        configured to collapse inwardly in response to pressure outside        of the proximal portion of the tube exceeding pressure inside        the proximal portion of the tube;    -   a pump disposed within the frame and configured to pump blood        through the tube from the subject's left ventricle to the        subject's aorta, such that, the proximal portion of the tube is        maintained in an open state when blood pressure generated within        the proximal portion of the tube by the blood pump exceeds        aortic pressure of the subject outside the proximal portion of        the tube; and    -   a plurality of elongate commissure elements that are disposed        within the proximal portion of the tube, such that, when the        proximal portion of the tube collapses inwardly, respective        portions of a circumference of the tube form cusps that contact        each other.        Inventive concept 89. The apparatus according to inventive        concept 88, further comprising a computer processor that is        configured to control pumping of blood through the tube by the        blood pump, such that blood pressure generated by the blood pump        within the tube exceeds systolic aortic pressure of the subject,        and is less than diastolic aortic pressure of the subject.        Inventive concept 90. The apparatus according to inventive        concept 88, further comprising a pressure sensor configured to        measure aortic blood pressure of the subject, and wherein the        computer processor is configured to receive an indication of the        measured aortic blood pressure, and to control pumping of blood        through the tube by the blood pump responsively to the measured        aortic blood pressure.        Inventive concept 91. The apparatus according to inventive        concept 88, further comprising a pressure sensor configured to        measure left-ventricular blood pressure of the subject, and        wherein the computer processor is configured to receive an        indication of the measured left-ventricular blood pressure, and        to control pumping of blood through the tube by the blood pump        responsively to the measured left-ventricular blood pressure.        Inventive concept 92. Apparatus, for use with a delivery device,        the apparatus comprising:

an impeller;

a frame disposed around the impeller,

-   -   the impeller and the frame being configured to be inserted into        a blood vessel of a subject via the delivery device, while        disposed in radially-constrained configurations thereof, and to        assume non-radially-constrained configuration by being released        from the delivery device; and

a coupling element comprising a first portion disposed upon theimpeller, and a second portion disposed on the frame and configured toengage with the first portion, the coupling element being configured tofacilitate radial constriction of the impeller by holding an end of theimpeller such that the impeller can be axially elongated, withoutradially constricting the frame.

Inventive concept 93. Apparatus comprising:

a blood-pump tube;

an impeller configured to be disposed within the blood-pump tube, and topump blood from a first location to a second location by pumping bloodthrough the blood-pump tube:

a motor disposed outside the subject's body, and configured to drive theimpeller to rotate;

a drive cable extending from outside the subject's body to the axialshaft, and configured to impart rotational motion from the motor to theimpeller, by rotating;

an outer tube disposed around the drive cable configured to extend fromoutside the subject's body to within the blood-pump tube, the outer tubedefining first and second openings on a portion of the outer tubedisposed within the blood-pump tube; and

a flow obstacle disposed over the first opening, such that the firstopening is configured to function as a stagnation pressure tap, and thesecond opening is configured to function as a static pressure tap;

at least one pressure sensor configured to measure pressure within thestagnation pressure tap and pressure within the static pressure tap; and

a computer processor configured to determine flow through the blood-pumptube, at least partially based upon the pressure measured within thestagnation pressure tap and the pressure measured within the staticpressure tap.

Inventive concept 94. A method comprising:

inserting a blood pump into a body of subject, the blood pump including:

-   -   an impeller that includes proximal and distal bushings,    -   a frame disposed around the impeller, the frame including        proximal and distal bearings, and    -   an axial shaft that passes through the proximal and distal        bearings of the frame and the proximal and distal bushings of        the impeller, the proximal bushing of the impeller being coupled        to the axial shaft, such that the proximal bushing is held in an        axially-fixed position with respect to the axial shaft, and the        distal bushing of the impeller not being coupled to the axial        shaft, such that the distal bushing is not held in an        axially-fixed position with respect to the axial shaft,        -   the impeller being maintained in a radially-constrained            configuration by a delivery catheter while the impeller is            inserted into the subject's body;

when the impeller is disposed within the subject's body, causing theimpeller to change from its radially-constrained configuration to anon-radially-constrained configuration by allowing the distal bushing toslide over the axial shaft, by releasing the impeller from the catheter;and

pumping blood through the subject's body using the impeller, while theimpeller is disposed in its non-radially-constrained configuration.

Inventive concept 95. A method comprising:

placing an impeller of a ventricular assist device inside a leftventricle of a subject, with a frame disposed around the impeller; and

driving the impeller to pump blood from the left ventricle to an aortaof the subject, by rotating the impeller,

placement of the impeller inside the left ventricle being such that theimpeller is allowed to undergo axial motion with respect to the frame,in response to cyclical changes in a pressure difference between theleft ventricle and the aorta.

Inventive concept 96. A method comprising:

placing a blood pump inside a body of a subject the blood pumpincluding:

-   -   an impeller with a frame disposed around the impeller, the        impeller including proximal and distal bushings, and the frame        including proximal and distal bearings, and    -   an axial shaft that passes through the proximal and distal        bearings of the frame and the proximal and distal bushings of        the impeller, the axial shaft being coupled to at least one of        the proximal and distal bushings of the impeller, such that the        at least one bushing is held in an axially-fixed position with        respect to the axial shaft, and not being held in an        axially-fixed position with respect to the proximal and distal        bearings; and

pumping blood through the subject's body, using the impeller.

Inventive concept 97. A method comprising:

placing an impeller of a blood pump inside a body of a subject, with aframe disposed around the impeller; and

driving the impeller to pump blood through the subject's body, withoutusing any thrust bearing disposed within the subject's body to provideopposition to thrust generated by the rotation of the impeller.

The present invention will be more fully understood from the followingdetailed description of embodiments thereof, taken together with thedrawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic illustrations of a ventricular assistdevice, a distal end of which is disposed in a subject's left ventricle,in accordance with some applications of the present invention;

FIGS. 2A, 2B, and 2C are schematic illustrations of a pump portion of aventricular assist device, in accordance with some applications of thepresent invention;

FIGS. 3A, 3B and, 3C are schematic illustrations of an impeller of aventricular assist device, in accordance with some applications of thepresent invention;

FIG. 4 is a schematic illustration of an impeller disposed inside aframe of a ventricular assist device, in accordance with someapplications of the present invention;

FIGS. 5A and 5B are schematic illustrations of the impeller and theframe of the ventricular assist device, respectively innon-radially-constrained and radially-constrained states thereof, inaccordance with some applications of the present invention;

FIG. 5C is a schematic illustration of a typical bearing assembly thatis used in prior art axial impeller-based blood pumps;

FIGS. 6A and 6B are schematic illustrations of a ventricular assistdevice at respective stages of a motion cycle of the impeller of theventricular assist device with respect to the frame of the ventricularassist device, in accordance with some applications of the presentinvention;

FIG. 6C is a schematic illustration of an axial-shaft-receiving tube anda distal tip portion of a ventricular assist device, in accordance withsome applications of the present invention;

FIG. 7 is a schematic illustration of a motor unit of a ventricularassist device, in accordance with some applications of the presentinvention;

FIGS. 8A and 8B are schematic illustrations of a motor unit of aventricular assist device, in accordance with some applications of thepresent invention;

FIG. 9 is a graph indicating variations in the length of a drive cableof a ventricular assist device as a pressure gradient against which theimpeller of the blood pump varies, as measured in experiments performedby the inventors of the present application;

FIGS. 10A, 10B, and 10C are schematic illustrations of a drive cable ofa ventricular assist device, in accordance with some applications of thepresent invention;

FIGS. 11A, and 11B are schematic illustrations of an interface componentthat forms an interface between respective portions of the drive cableof the ventricular assist device, in accordance with some applicationsof the present invention;

FIGS. 11C, 11D, and 11E are schematic illustrations of an interfacebetween the drive cable and an axial shaft of the ventricular assistdevice, in accordance with some applications of the present invention;

FIG. 12 is a schematic illustration of a drive cable of a ventricularassist device that includes friction-reduction elements disposed aroundat least a portion of the drive cable, in accordance with someapplications of the present invention;

FIG. 13 is a schematic illustration of a procedure for purging a drivecable and/or radial bearings of a ventricular assist device, inaccordance with some applications of the present invention;

FIGS. 14A and 14B are schematic illustrations of a frame of aventricular assist device, a stator being coupled to a proximal portionof the frame, in accordance with some applications of the presentinvention;

FIG. 15A is a schematic illustration of a flattened profile of a frameof a ventricular assist device, in accordance with some applications ofthe present invention;

FIG. 15B is a schematic illustration showing an enlarged view of theproximal end of the frame of the ventricular assist device, inaccordance with some applications of the present invention;

FIG. 15C is a schematic illustration of the frame of the ventricularassist device, a material that defines curved projections being coupledto the frame, in accordance with some applications of the presentinvention;

FIGS. 16A, 16B, 16C and 16D are schematic illustrations of a ventricularassist device that includes one or more blood-pressure-measurementtubes, in accordance with some applications of the present invention;

FIGS. 17A, 17B, and 17C are schematic illustrations of a ventricularassist device that includes a pitot tube that is configured to measureblood flow through a tube of the device, in accordance with someapplications of the present invention;

FIG. 18 is a schematic illustration of a ventricular assist device, atip portion of the device, being a radially-expandable atraumatic distaltip portion, in accordance with some applications of the presentinvention;

FIGS. 19A and 19B are schematic illustrations of a ventricular assistdevice, a tip portion of the device, being a radially-expandableatraumatic distal tip portion, in accordance with some applications ofthe present invention;

FIGS. 20A and 20B are schematic illustrations of a ventricular assistdevice, a tip portion of the device, being a radially-expandableatraumatic distal tip portion, in accordance with some applications ofthe present invention;

FIGS. 21A, 21B, 21C, and 21D are schematic illustrations of a distal tipportion of a ventricular assist device, in accordance with someapplications of the present invention;

FIGS. 22A and 22B are schematic illustrations of a distal tip portion ofa ventricular assist device, respectively, in an axially-stiffenedconfiguration and a non-axially-stiffened configuration, in accordancewith some applications of the present invention;

FIGS. 23A and 23B are schematic illustrations of a distal tip portion ofa ventricular assist device, respectively, in a radially-constrainedconfiguration and a non-radially-constrained configuration, inaccordance with some applications of the present invention;

FIGS. 24A and 24B are schematic illustrations of a distal tip portion ofa ventricular assist device, respectively, in a radially-constrainedconfiguration and a non-radially-constrained configuration, inaccordance with some applications of the present invention;

FIG. 25A is a schematic illustration of a first portion and a secondportion of a coupling element configured to facilitate radialconstriction (e.g., during crimping) of an impeller, in accordance withsome applications of the present invention;

FIGS. 25B and 25C are schematic illustrations of respective stages ofthe crimping of the impeller, in accordance with some applications ofthe present invention;

FIG. 26 is a schematic illustration of a stopper configured to preventdistal advancement of an impeller of a ventricular assist device duringwithdrawal of the ventricular assist device from the subject's body, inaccordance with some applications of the present invention;

FIGS. 27A and 27B are schematic illustrations of a ventricular assistdevice, the device including a valve to prevent backflow of blood, forexample, in the event that an impeller of the ventricular assist devicemalfunctions, in accordance with some applications of the presentinvention; and

FIGS. 28A, 28B, and 28C are schematic illustrations of a ventricularassist device, the device including a safety balloon to prevent backflowof blood, for example, in the event that an impeller of the ventricularassist device malfunctions, in accordance with some applications of thepresent invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Reference is now made to FIGS. 1A and 1B, which are schematicillustrations of a ventricular assist device 20, a distal end of whichis disposed in a subject's left ventricle 22, in accordance with someapplications of the present invention. The ventricular assist deviceincludes a tube 24, which traverses an aortic valve 26 of the subject,such that a proximal end 28 of the tube is disposed in an aorta 30 ofthe subject and a distal end 32 of the tube is disposed within leftventricle 22. Tube 24 (which is sometimes referred to herein as a“blood-pump tube”) is typically an elongate tube, an axial length of thetube typically being substantially larger than its diameter. The scopeof the present invention includes using the apparatus and methodsdescribed herein in anatomical locations other than the left ventricleand the aorta. Therefore, the ventricular assist device and/or portionsthereof are sometimes referred to herein (in the specification and theclaims) as a blood pump.

As shown in FIG. 1B, which shows steps in the deployment of theventricular assist device in the left ventricle, typically the distalend of the ventricular assist device is guided to the left ventricleover a guidewire 10. During the insertion of the distal end of thedevice to the left ventricle, a delivery catheter 143 is disposed overthe distal end of the device. Once the distal end of the device isdisposed in the left ventricle, the delivery catheter is typicallyretracted to the aorta, and the guidewire is withdrawn from thesubject's body. The retraction of the delivery catheter typically causesself-expandable components of the distal end of the device to assumenon-radially-constrained configurations, as described in further detailhereinbelow. Typically, the ventricular assist device is inserted intothe subject's body in order to provide an acute treatment to thesubject. For some applications, in order to withdraw the leftventricular device from the subject's body at the end of the treatment,the delivery catheter is advanced over the distal end of the device,which causes the self-expandable components of the distal end of thedevice to assume radially-constrained configurations. Alternatively oradditionally, the distal end of the device is retracted into thedelivery catheter which causes the self-expandable components of thedistal end of the device to assume radially-constrained configurations.

Reference is also made to FIGS. 2A, 2B, and 2C, which are schematicillustrations of a blood pump portion 27 of ventricular assist device20, in accordance with some applications of the present invention.Typically, an impeller 50 is disposed within a distal portion 102 oftube 24 and is configured to pump blood from the left ventricle into theaorta by rotating. The tube typically defines one or more blood inletopenings 108 at the distal end of the tube, via which blood flows intothe tube from the left ventricle, during operation of the impeller. Forsome applications, the proximal portion of the tube defines one or moreblood outlet openings 109, via which blood flows from the tube into theascending aorta, during operation of the impeller.

For some applications, a control console 21, which typically includes acomputer processor 25 (shown in FIG. 1A), drives the impeller to rotate.For example, the computer processor may control a motor 74 (shown inFIG. 7 ), which is disposed within a motor unit 23 and which drives theimpeller to rotate via a drive cable 130 (also shown in FIG. 7 ). Forsome applications, the computer processor is configured to detect aphysiological parameter of the subject (such as left-ventricularpressure, cardiac afterload, etc.) and to control rotation of theimpeller in response thereto, as described in further detailhereinbelow. Typically, the operations described herein that areperformed by the computer processor, transform the physical state of amemory, which is a real physical article that is in communication withthe computer processor, to have a different magnetic polarity,electrical charge, or the like, depending on the technology of thememory that is used. Computer processor 25 is typically a hardwaredevice programmed with computer program instructions to produce aspecial-purpose computer. For example, when programmed to perform thetechniques described herein, computer processor 25 typically acts as aspecial-purpose, ventricular-assist computer processor.

For some applications, a purging system 29 drives a fluid (e.g., aglucose solution) to pass through portions of ventricular assist device20, for example, in order to cool portions of the device and/or in orderto wash debris from portions of the device. Purging system 29 isdescribed in further detail hereinbelow.

Typically, along distal portion 102 of tube 24, a frame 34 is disposedwithin the tube. The frame is typically made of a shape-memory alloy,such as nitinol. For some applications, the shape-memory alloy of theframe is shape set such that the frame (and thereby the tube) assumes agenerally circular, elliptical, or polygonal cross-sectional shape inthe absence of any forces being applied to the tube. By assuming itsgenerally circular, elliptical, or polygonal cross-sectional shape, theframe is configured to hold the distal portion of the tube in an openstate. Typically, during operation of the ventricular assist device, thedistal portion of the tube is configured to be placed within thesubject's body, such that the distal portion of the tube is disposed atleast partially within the left ventricle.

For some applications (not shown), during operation of the ventricularassist device, the distal portion of the tube is disposed at leastpartially within the native aortic valve and the frame is configured tohold open the aortic valve, by assuming its generally circular,elliptical, or polygonal cross-sectional shape. For some applications,tube 24 is sized such as to prevent the shape-memory alloy of frame 34from fully assuming the dimensions to which the shape-memory alloy wasshape set. In this manner, the frame is “pre-tensioned,” such that evenif the aortic valve applies a radially compressive force to the tube andthe frame, the frame does not become radially compressed, since theframe is already being maintained in a partial radially-constrainedstate by the tube. For some applications, the frame includes a pluralityof rigid struts 111 that are disposed in parallel to each other, and inparallel to the longitudinal axis of the frame. The rigid struts areconfigured such that at least a portion 110 of the frame along which thestruts are disposed maintains a substantially straight longitudinalaxis, even when subjected to anatomical forces within the left ventricleand/or the aortic valve. Typically, rigid struts are configured suchthat even as frame 34 changes from a radially-constrained configuration(in which the frame is typically disposed during introduction of theframe into the subject's body) to a non-radially-constrainedconfiguration (in which the frame is typically disposed during operationof the ventricular assist device), the lengths of the rigid struts donot change.

For some applications, along a proximal portion 106 of tube 24, theframe is not disposed within the tube, and the tube is therefore notsupported in an open state by frame 34. Tube 24 is typically made of ablood-impermeable collapsible material. For example, tube 24 may includepolyurethane, polyester, and/or silicone. Typically, the proximalportion of the tube is configured to be placed such that it is at leastpartially disposed within the subject's ascending aorta. For someapplications, the proximal portion of the tube traverses the subject'saortic valve, passing from the subject's left ventricle into thesubject's ascending aorta, as shown in FIG. 1B. As describedhereinabove, the tube typically defines one or more blood inlet openings108 at the distal end of the tube, via which blood flows into the tubefrom the left ventricle, during operation of the impeller. For someapplications, the proximal portion of the tube defines one or more bloodoutlet openings 109, via which blood flows from the tube into theascending aorta, during operation of the impeller. Typically, the tubedefines a plurality of blood outlet openings 109, for example, betweentwo and eight blood outlet openings (e.g., between two and four bloodoutlet openings). During operation of the impeller, the pressure of theblood flow through the tube typically maintains the proximal portion ofthe tube in an open state. For some applications, in the event that, forexample, the impeller malfunctions, the proximal portion of the tube isconfigured to collapse inwardly, in response to pressure outside of theproximal portion of the tube exceeding pressure inside the proximalportion of the tube. In this manner, the proximal portion of the tubeacts as a safety valve, preventing retrograde blood flow into the leftventricle from the aorta.

For some applications, computer processor 25 of control console 21(shown in FIG. 1A) is configured to control pumping of the blood pump(e.g., by controlling rotation of the impeller) such that the bloodpressure generated by the pump within tube 24 exceeds the subject'ssystolic aortic pressure during systole, but is less than the subject'sdiastolic aortic pressure during diastole. During systole, proximalportion 106 of tube 24 is held open since the blood pressure within thetube exceeds the aortic pressure exerted upon the tube from outside thetube. During diastole, the proximal portion of tube 24 closes, since theaortic pressure exerted upon the tube from outside the tube exceedsblood pressure within the tube. In this manner, the impeller pumps bloodfrom the left ventricle to the aorta in a pulsatile manner (i.e., byonly pumping blood from the left ventricle to the aorta duringdiastole). For some applications, the computer processor is configuredto measure the subject's aortic pressure, left-ventricular pressure,and/or flow through tube 24 for example using techniques as describedhereinbelow with reference to FIGS. 9, 16A-D, and/or 17. For some suchapplications, based upon the measured aortic pressure, left-ventricularpressure, and/or flow, the computer processor controls rotation of theimpeller in the above-described manner. Alternatively, the computerprocessor controls rotation of the impeller, based upon the measuredaortic pressure, left-ventricular pressure, and/or flow in a differentmanner from the above-described manner. For example, the computerprocessor may be configured to change the rate of rotation of theimpeller based upon the measured aortic pressure, left-ventricularpressure, and/or flow, but in a manner that results in the impellerpumping blood from the left ventricle to the aorta in a non-pulsatile,continuous manner.

Typically, pumping of blood by the impeller increases aortic pressureand reduces left-ventricular pressure. Once flow through tube 24 reachesa critical value above which aortic pressure is higher thanleft-ventricular pressure even in ventricular systole (hereinafter“systole”), the aortic valve remains closed around the outside of tube24 throughout the cardiac cycle and flow from the ventricle to the aortaoccurs exclusively via the tube. Typically, above this point ofuncoupling aortic from ventricular pressure, the left ventricle nolonger performs net external work (defined as volume change timespressure change), as it is not moving any volume. In this mode, oxygenconsumption by the left ventricle depends on cyclic pressure generationagainst a closed aortic valve, wall tension that results from the sizeof the left ventricle, wall thickness, as well as baseline metabolicdemands (including calcium cycling). Below this critical point ofimpeller activity, the aortic valve is typically at least partially openin systole and left ventricular outflow will occur both between theoutside of the tube and the aortic valve (by virtue of left ventricularcontraction) as well as through the tube (by virtue of the impellerrotating and pumping). For a given number of impeller revolutions perminute, flow through the tube will typically be greater the larger thecross-sectional area of the sleeve. At the same time, the larger thecross-sectional area of the tube, the more space the tube occupieswithin the left ventricular outflow tract, the smaller the remainingoutflow area, and consequently, the higher the outflow resistance theleft ventricle has to overcome for pumping around the outside of thetube.

Hence, typically, a trade-off exists between the efficiency of theimpeller in assisting the left ventricle (which favorably increases withtube diameter) and the residual resistance to outflow around the outsideof the tube 24 (which unfavorably increases with tube diameter). Thehigher the flow through the tube provided by the impeller (for a giventube diameter), the less the effect of the reduced cross-sectionaloutflow area on effective outflow resistance may matter, as theremaining cross-sectional area may be appropriate for the residual smallstroke volume that the ventricle has to eject, i.e., the reducedresidual outflow tract area may not pose an undue resistance to outflow.Conversely, however, once a fixed tube diameter is selected, effectiveresistance to outflow increases as flow through the tube decreases,since a larger proportion of left ventricular stroke volume now needs topass the residual outflow tract area around the tube. Therefore, forsome applications, left ventricular outflow resistance is configured toautomatically adjust in order to compensate for changes in the bloodflow through the tube that is generated by the impeller. For example,the tube may be made of a compliant material, the compliance of which issuch that a decrease in flow through the tube, and the subsequent dropin distending pressure, results in a decrease in sleeve diameter,thereby increasing the outflow area available for the left ventricle.Typically, the material properties of the compliant material are definedsuch that (a) maximum tube expansion is reached just at, or close to,the point when the pump-flow-generated intraluminal pressure exceedsaortic pressure (irrespective of the point in the cardiac cycle) andhence remains above left-ventricular pressure throughout the cardiaccycle, and (b) full collapse of the tube is reached when flow throughthe tube that is generated by the impeller becomes zero.

Referring now to FIG. 2B, for some applications, a plurality of elongatecommissure elements 107 extend along at least some of proximal portion106 of tube 24. As described hereinabove, for some applications,computer processor 25 is configured to drive impeller 50 to pump bloodfrom the left ventricle to the aorta in a pulsatile manner. For someapplications, the commissure elements are configured to facilitateopening and closing of the proximal portion of the tube in a manner thatis similar to the opening and closing of native valve leaflets, withrespective portions of the circumference of the tube forming cusps thatcontact each other when the tube closes. For some applications, theventricular assist device includes three elongate commissure elements,and the proximal portion of tube 24 is configured to close in a mannerthat is similar to that of a tri-leaflet valve. (FIG. 2B depicts such anembodiment, but one of the commissure elements is hidden from view.) Forsome applications (not shown), the ventricular assist device includestwo elongate commissure elements, and the proximal portion of tube 24 isconfigured to close in a manner that is similar to that of a bi-leafletvalve. For some applications, the proximal portion of tube 24 is placedsuch as to traverse the subject's aortic valve, and the commissureelements are rotationally aligned with the commissures of the nativevalve. In this manner, the artificial cusps of the proximal portion ofthe tube are aligned with the native aortic valve leaflets.

Referring to FIGS. 2A-C, for some applications, frame 34 is shaped suchthat the frame defines a proximal conical portion 36, a centralcylindrical portion 38, and a distal conical portion 40. Typically, theproximal conical portion is such that the narrow end of the cone isproximal with respect to the wide end of the cone. Further typically,the distal conical portion is such that the narrow end of the cone isdistal with respect to the wide end of the cone. For some applications,tube 24 extends to the end of cylindrical portion 38, such that thedistal end of the tube defines a single axially-facing blood inletopening 108, as shown in FIGS. 2A and 2B. Alternatively, tube 24 extendsto the end of distal conical portion 40, and the tube defines one ormore lateral blood inlet openings, as shown in FIG. 2C. For suchapplications, the tube typically defines two to four lateral blood inletopenings.

Typically, tube 24 includes a conical proximal portion 42 and acylindrical central portion 44. The proximal conical portion istypically such that the narrow end of the cone is proximal with respectto the wide end of the cone. As described hereinabove, for someapplications, the tube extends to the end of distal conical portion 40of frame 34. For such applications, the tube typically defines a distalconical portion 46, with the narrow end of the cone being distal withrespect to the wide end of the cone, as shown in FIG. 2C. For someapplications (not shown), the diameter of tube 24 changes along thelength of the central portion of the tube, such that the central portionof the tube has a frustoconical shape. For example, the central portionof the tube may widen from its proximal end to is distal end, or maynarrow from its proximal end to its distal end. For some applications,at its proximal end, the central portion of the tube has a diameter ofbetween 5 and 7 mm, and at its distal end, the central portion of thetube has a diameter of between 8 and 12 mm.

Reference is now made to FIGS. 3A-C, which are schematic illustrationsof impeller 50, in accordance with some applications of the presentinvention. Typically, the impeller includes at least one outer helicalelongate element 52, which winds around a central axial spring 54, suchthat the helix defined by the helical elongate element is coaxial withthe central axial spring. Typically, the impeller includes two or morehelical elongate elements (e.g., three helical elongate elements, asshown in FIGS. 3A-C). For some applications, the helical elongateelements and the central axial spring are made of a shape-memorymaterial, e.g., a shape-memory alloy such as nitinol. Typically, each ofthe helical elongate elements and the central axial spring support afilm 56 of a material (e.g., a polymer, such as polyurethane, and/orsilicone) therebetween. For illustrative purposes, the impeller is shownin the absence of the material in FIG. 3A. FIGS. 3B and 3C showrespective views of the impeller with the material supported between thehelical elongate elements and the spring.

Each of the helical elongate elements, together with the film extendingfrom the helical elongate element to the spring, defines a respectiveimpeller blade, with the helical elongate elements defining the outeredges of the blades, and the axial spring defining the axis of theimpeller. Typically, the film of material extends along and coats thespring. For some applications, sutures 53 (e.g., polyester sutures,shown in FIGS. 3B and 3C) are wound around the helical elongateelements, e.g., as described in US 2016/0022890 to Schwammenthal, whichis incorporated herein by reference. Typically, the sutures areconfigured to facilitate bonding between the film of material (which istypically a polymer, such as polyurethane, or silicone) and the helicalelongate element (which is typically a shape-memory alloy, such asnitinol). For some applications, sutures (e.g., polyester sutures, notshown) are wound around spring 54. Typically, the sutures are configuredto facilitate bonding between the film of material (which is typically apolymer, such as polyurethane, or silicone) and the spring (which istypically a shape-memory alloy, such as nitinol).

Typically, proximal ends of spring 54 and helical elongate elements 52extend from a proximal bushing (i.e., sleeve bearing) 64 of theimpeller, such that the proximal ends of spring 54 and helical elongateelements 52 are disposed at a similar radial distance from thelongitudinal axis of the impeller, as each other. Similarly, typically,distal ends of spring 54 and helical elongate elements 52 extend from adistal bushing 58 of the impeller, such that the distal ends of spring54 and helical elongate elements 52 are disposed at a similar radialdistance from the longitudinal axis of the impeller, as each other.Typically, spring 54, as well as proximal bushing 64 and distal bushing58 of the impeller, define a lumen 62 therethrough.

Reference is now made to FIG. 4 , which is a schematic illustration ofimpeller 50 disposed inside frame 34 of ventricular assist device 20, inaccordance with some applications of the present invention. As shown,typically there is a gap G, between the outer edge of impeller 50 andthe inner surface of frame 34, even at a location at which the span ofthe impeller is at its maximum. For some applications, it is desirablethat the gap between the outer edge of the blade of the impeller and theinner surface of frame 34 be relatively small, in order for the impellerto efficiently pump blood from the subject's left ventricle into thesubject's aorta. However, it is also desirable that a gap between theouter edge of the blade of the impeller and the inner surface of frame34 be maintained, for example, in order to reduce the risk of hemolysis.

For some applications, the gap G between the outer edge of the impellerand the inner surface of frame 34, at the location at which the span ofthe impeller is at its maximum, is greater than 0.05 min (e.g., greaterthan 0.1 mm), and/or less than 1 mm (e.g., less than 0.4 mm), e.g., 0.05mm-1 mm, or 0.1 mm-0.4 mm. For some applications, the outer diameter ofthe impeller at the location at which the outer diameter of the impelleris at its maximum is more than 6 mm (e.g., more than 6.5 mm), and/orless than 8 mm (e.g., less than 7 mm), e.g., 6-8 mm, or 6.5-7 mm. Forsome applications, the inner diameter of frame 34 is more than 6.5 mm(e.g. more than 7 mm), and/or less than 8.5 mm (e.g., less than 7.5 mm),e.g., 6.5-8.5 mm, or 7-7.5 mm.

Typically, an axial shaft 92 passes through the axis of impeller 50, vialumen 62 of the impeller. Typically, proximal bushing 64 of the impelleris coupled to the shaft such that the axial position of the proximalbushing with respect to the shaft is fixed, and distal bushing 58 of theimpeller is slidable with respect to the shaft. The axial shaft itselfis radially stabilized via a proximal radial bearing 116 and a distalradial bearing 118, defined by frame 34. In turn, the axial shaft, bypassing through lumen 62 defined by the impeller, radially stabilizesthe impeller with respect to the inner surface of frame 34, such thateven a relatively small gap between the outer edge of the blade of theimpeller and the inner surface of frame 34 (e.g., a gap that is asdescribed above) is maintained, during rotation of the impeller.

Referring again to FIGS. 3A-C, for some applications, the impellerincludes a plurality of elongate elements 67 extending radially fromcentral axial spring 54 to outer helical elongate elements 52. Theelongate elements are typically flexible but are substantiallynon-stretchable along the axis defined by the elongate elements. Furthertypically, each of the elongate elements is configured not to exertforce upon the helical elongate element, unless force is acting upon theimpeller that is causing the helical elongate element to move radiallyoutward such that (in the absence of the elongate element) a separationbetween the helical elongate element and the central axial spring wouldbe greater than a length of the elongate element. For example, theelongate elements may include strings (such as polyester, and/or anotherpolymer or a natural material that contains fibers) and/or wires (suchas nitinol wires, and/or wires made of a different alloy, or a metal).

For some applications, the elongate elements 67 maintain the helicalelongate element (which defines the outer edge of the impeller blade)within a given distance with respect to the central axial spring. Inthis manner, the elongate elements are configured to prevent the outeredge of the impeller from being forced radially outward due to forcesexerted upon the impeller during the rotation of the impeller. Theelongate elements are thereby configured to maintain the gap between theouter edge of the blade of the impeller and the inner surface of frame34, during rotation of the impeller. Typically, more than one (e.g.,more than two) and/or fewer than eight (e.g., fewer than four) elongateelements 67 are use in the impeller, with each of the elongate elementstypically being doubled (i.e., extending radially from central axialspring 54 to an outer helical elongate element 52, and then returningfrom the helical elongate element back to the central axial spring). Forsome applications, a plurality of elongate elements, each of whichextends from the spring to a respective helical elongate element andback to the spring, are formed from a single piece of string or a singlewire, as described in further detail hereinbelow.

For some applications, the impeller is manufactured in the followingmanner Proximal bushing 64, distal bushing 58, and helical elongateelements 52 are cut from a tube of shape-memory material, such asnitinol. The cutting of the tube, as well as the shape setting of theshape-memory material, is typically performed such that the helicalelongate elements are defined by the shape-memory material, e.g., usinggenerally similar techniques to those described in US 2016/0022890 toSchwammenthal. Typically, spring 54 is inserted into the cut andshape-set tube, such that the spring extends along the length of thetube from at least the proximal bushing to the distal bushing. For someapplications, the spring is inserted into the cut and shape-set tubewhile the spring is in an axially compressed state, and the spring isconfigured to be held in position with respect to the tube, by exertinga radial force upon the proximal and distal bushings. Alternatively oradditionally, portions of the spring are welded to the proximal anddistal bushings. For some applications, the spring is cut from a tube ofa shape-memory material, such as nitinol. For some such applications,the spring is configured such that, when the spring is disposed in anon-radially-constrained configuration (in which the spring is typicallydisposed during operation of the impeller), there are substantially nogaps between windings of the spring and adjacent windings thereto.

For some applications, at this stage, elongate elements 67, as describedhereinabove, are placed such as to extend between the spring and one ormore of the helical elongate elements, for example, in the followingmanner A mandrel (e.g., a polyether ether ketone (PEEK) and/or apolytetrafluoroethylene (PTFE) mandrel) is inserted through the lumendefined by the spring and the bushings. A string or a wire is thenthreaded such that it passes (a) from the mandrel to a first one of thehelical elongate elements, (b) back from the first of the helicalelongate elements to the mandrel, (c) around the mandrel, and to asecond one of the helical elongate elements, (d) back from the secondone of the helical elongate elements to the mandrel, etc. Once thestring or the wire has been threaded from the mandrel to each of thehelical elongate elements and back again, the ends of the string or thewire are coupled to each other, e.g., by tying them to each other. Forsome applications, sutures 53 (e.g., polyester sutures) are wound aroundthe helical elongate elements, in order to facilitate bonding betweenthe film of material (which is typically a polymer, such aspolyurethane, or silicone) and the helical elongate elements (which istypically a shape-memory alloy, such as nitinol), in a subsequent stageof the manufacture of the impeller. For some applications, sutures(e.g., polyester sutures, not shown) are wound around spring 54.Typically, the sutures are configured to facilitate bonding between thefilm of material (which is typically a polymer, such as polyurethane, orsilicone) and the spring (which is typically a shape-memory alloy, suchas nitinol), in the subsequent stage of the manufacture of the impeller.

Typically, at this stage, a structure 59 has been assembled that is asshown in FIG. 3A. The structure includes the cut and shape-set tube thatdefines the proximal and distal bushing and helical elongate elements,the spring, and optionally the elongate elements, and the sutures. Thisstructure is dipped into the material that defines film 56. For someapplications, the assembled structure is dipped into the material withthe mandrel disposed through the lumen defined by the spring and thebushings, although it is noted that the mandrel is not shown in FIG. 3A.Typically, the material from which the film is made is silicone (and/ora similar polymer), and the assembled structure is dipped into thematerial, while the material is in an uncured, liquid state.Subsequently, the material is cured such that it solidifies, e.g., bybeing left to dry. Once the material has dried, the mandrel is typicallyremoved from the lumen defined by the bushings and the spring.

The result of the process described above is typically that there is acontinuous film of material extending between each of the helicalelongate elements to the spring, and also extending along the length ofthe spring, such as to define a tube, with the spring embedded withinthe tube. The portions of the film that extend from each of the helicalelongate elements to the spring define the impeller blades. Forapplications, in which the impeller includes elongate elements 67, theelongate elements are typically embedded within these portions of film.

Typically, impeller 50 is inserted into the left ventricletranscatheterally, while impeller 50 is in a radially-constrainedconfiguration. In the radially-constrained configuration, both helicalelongate elements 52 and central axial spring 54 become axiallyelongated, and radially constrained. Typically film 56 of the material(e.g., silicone) changes shape to conform to the shape changes of thehelical elongate elements and the axial support spring, both of whichsupport the film of material. Typically, using a spring to support theinner edge of the film allows the film to change shape without the filmbecoming broken or collapsing, due to the spring providing a largesurface area to which the inner edge of the film bonds. For someapplications, using a spring to support the inner edge of the filmreduces a diameter to which the impeller can be radially constrained,relative to if, for example, a rigid shaft were to be used to supportthe inner edge of the film, since the diameter of the spring itself canbe reduced by axially elongating the spring.

As described hereinabove, for some applications, proximal bushing 64 ofimpeller 50 is coupled to axial shaft 92 such that the axial position ofthe proximal bushing with respect to the shaft is fixed, and distalbushing 58 of the impeller is slidable with respect to the shaft. Forsome applications, when the impeller is radially constrained for thepurpose of inserting the impeller into the ventricle or for the purposeof withdrawing the impeller from the subject's body, the impelleraxially elongates by the distal bushing sliding along the axial shaftdistally.

Subsequent to being released inside the subject's body, the impellerassumes its non-radially-constrained configuration (in which theimpeller is typically disposed during operation of the impeller), asshown in FIGS. 3A-C. Typically, the pitch of each of the helicalelongate elements 52, when impeller 50 is in a non-radially-constrainedconfiguration (e.g., inside the subject's ventricle), is greater than 1mm (e.g., greater than 6 mm), and/or less than 20 mm (e.g., less than 10mm). Typically, ceteris paribus, the greater the pitch of the helicalelongate element (and therefore the impeller blade), the greater theblood flow that is generated by the impeller. Therefore, as described,the pitch of the helical elongate elements 52, when impeller 50 is inthe non-radially-constrained configuration, is typically greater than 1mm (e.g., greater than 6 mm). On the other hand, it is typicallydesirable that the impeller occludes backflow of blood into thesubject's left ventricle. Ceteris paribus, it is typically the case thatthe smaller the pitch of the helical elongate element (and therefore theimpeller blade), the greater the occlusion that is provided by theimpeller. Therefore, as described, the pitch of the helical elongateelements 52, when impeller 50 is in the non-radially-constrainedconfiguration, is typically less than 20 mm (e.g., less than 10 mm).

For some applications, the pitch of the helical elongate elements (andtherefore the impeller blade) varies along the length of the helicalelongate element, at least when the impeller is in anon-radially-constrained configuration. Typically, for suchapplications, the pitch increases from the distal end of the impeller(i.e., the end that is inserted further into the subject's body, andthat is placed upstream with respect to the direction of antegrade bloodflow) to the proximal end of the impeller (i.e., the end that is placeddownstream with respect to the direction of antegrade blood flow), suchthat the pitch increases in the direction of the blood flow. Typically,the blood flow velocity increases along the impeller, along thedirection of blood flow. Therefore, the pitch is increased along thedirection of the blood flow, such as to further accelerate the blood.

It is noted that, for illustrative purposes, in some of the figures,impeller 50 is shown without including all of the features of theimpeller as shown and described with respect to FIGS. 3A-C. For example,some of the figures show the impeller not including sutures 53 and/orelongate elements 67. The scope of the present application includesusing an impeller with any of the features shown and described withrespect to FIGS. 3A-C in combination with any of the apparatus andmethods described herein.

Reference is now made to FIGS. 5A and 5B, which are schematicillustrations of impeller 50 and frame 34 of ventricular assist device20, respectively in non-radially-constrained and radially-constrainedstates thereof, in accordance with some applications of the presentinvention. The impeller and the frame are typically disposed in theradially-constrained states during the transcatheteral insertion of theimpeller and the frame into the subject's body, and are disposed in thenon-radially-constrained states during operation of the impeller insidethe subject's left ventricle. As described hereinabove, typically tube24 extends from at least a distal portion of the frame and proximallytherefrom. However, for illustrative purposes, the frame and theimpeller are shown in the absence of tube 24 in FIGS. 5A-B. As indicatedin FIG. 5B, the frame and the impeller are typically maintained inradially-constrained configurations by delivery catheter 143.

Reference is also made to FIG. 5C, which shows a typical bearingassembly that is used in prior art axial impeller-based blood pumps.FIG. 5C is shown for the purpose of acting as a point of reference forsome of the applications of the invention described herein. As shown inFIG. 5C, a bearing assembly typically includes a radial bearing(indicated by ellipse 200) and a thrust bearing (indicated by circle202). The radial bearing is configured to reduce radial motion of theimpeller, by maintaining the axis of the impeller at a given radialposition. In response to an impeller pumping blood in a first direction,forces acting upon the impeller typically push the impeller to move inthe opposite direction to the first direction. The purpose of a thrustbearing is to oppose such motion of the impeller and to maintain theaxial position of the impeller. In the example shown in FIG. 5C, inresponse to the impeller pumping blood in the direction of arrow 204,the impeller gets pushed in the direction of arrow 206, and the thrustbearing opposes this motion. Typically, due to the frictional forcesthat are exerted upon them, bearings undergo a substantial amount ofheating and wear. Thrust bearings are typically exposed to substantialheating and wear, due to the fact that the frictional forces that areexerted upon them are typically spread over opposing surfaces having asmaller contact area between them, than is the case for radial bearings.

As described hereinabove, typically, axial shaft 92 passes through theaxis of impeller 50, via lumen 62 of the impeller. Typically, proximalbushing 64 of the impeller is coupled to the shaft via a couplingelement 65 such that the axial position of the proximal bushing withrespect to the shaft is fixed, and distal bushing 58 of the impeller isslidable with respect to the shaft. The axial shaft itself is radiallystabilized via a proximal radial bearing 116 and a distal radial bearing118, defined by frame 34. In turn, the axial shaft, by passing throughlumen 62 defined by the impeller, radially stabilizes the impeller withrespect to the inner surface of frame 34, such that even a relativelysmall gap between the outer edge of the blade of the impeller and theinner surface of frame 34 (e.g., a gap that is as described above) ismaintained, during rotation of the impeller, as described hereinabove.For some applications, axial shaft 92 is made of stainless steel, andproximal bearing 116 and/or distal bearing 118 are made of hardenedsteel. Typically, when crimping (i.e., radially constraining) theimpeller and the frame for the purpose of inserting the impeller and theframe into the subject's body, distal bushing 58 of the impeller isconfigured to slide along the axial shaft in the distal direction, suchthat the impeller becomes axially elongated, as described hereinabove.More generally, the impeller changes from its radially-constrainedconfiguration to its non-radially-constrained configuration, and viceversa, by the distal bushing sliding over the axial shaft.

Typically, the impeller itself is not directly disposed within anyradial bearings or thrust bearings. Rather, bearings 116 and 118 act asradial bearings with respect to the axial shaft. For some applications,there is no thrust bearing in contact with any surface that couldgenerate thrust forces during the rotation of the impeller, since theimpeller is configured to move axially within frame 34, while theimpeller is rotating, as described in further detail hereinbelow.Typically, pump portion 27 (and more generally ventricular assist device20) does not include any thrust bearing that is configured to bedisposed within the subject's body and that is configured to opposethrust generated by the rotation of the impeller. For some applications,one or more thrust bearings are disposed outside the subject's body(e.g., within motor unit 23, shown in FIGS. 1A, 7, and 8A-B), andopposition to thrust generated by the rotation of the impeller isprovided solely by the one or more thrust bearings disposed outside thesubject's body. For some applications, a mechanical element and/or amagnetic element is configured to maintain the impeller within a givenrange of axial positions. For example, a magnet (e.g., magnet 82,described hereinbelow with reference to FIG. 7 ) that is disposed at theproximal end of the drive cable (e.g., outside the subject's body) maybe configured to impart axial motion to the impeller, and to maintainthe impeller within a given range of axial positions.

For some alternative applications of the present invention, aventricular assist device includes an impeller that is not configured tomove in an axial back-and-forth motion. For some such applications (notshown), a thrust bearing is used to maintain the axial position of theimpeller, and the thrust bearing is disposed within a portion of theventricular assist device that is proximal to the impeller, such thatthe thrust bearing does not come into contact with the subject's blood.For example, the thrust bearing may be disposed within an outer tube inwhich the drive shaft of the impeller is disposed. Alternatively oradditionally, the thrust bearing may be disposed outside the subject'sbody. For some such applications, since the thrust bearing is disposedoutside the subject's body, the thrust bearing's dimensions are notconstrained by virtue of needing to be deployed within a smallanatomical location. Therefore, in such cases, the contact area betweenthe two opposing surfaces of the thrust bearing is typically greaterthan 20 square mm. For some applications (not shown), the thrust bearingis disposed distally to the impeller and in contact with the subject'sblood, such that the thrust bearing is cooled by the subject's blood.

Reference is now made to FIGS. 6A and 6B, which are schematicillustrations of ventricular assist device 20 at respective stages of amotion cycle of impeller 50 of the ventricular assist device withrespect to frame 34 of the ventricular assist device, in accordance withsome applications of the present invention. For some applications, whilethe impeller is pumping blood through tube 24, by rotating, axial shaft92 (to which the impeller is fixated) is driven to move the impelleraxially back-and-forth within frame 34, by the axial shaft moving in anaxial back-and-forth motion, as described in further detail hereinbelowwith reference to FIG. 7 . Alternatively or additionally, the impellerand the axial shaft are configured to move axially back-and-forth withinframe 34 in response to forces that are acting upon the impeller, andwithout requiring the axial shaft to be actively driven to move in theaxial back-and-forth motion, as described in further detail hereinbelow,for example, with reference to FIG. 9 .

For some applications, by moving in the back-and-forth motion, theportions of the axial shaft that are in contact with proximal bearing116 and distal bearing 118 are constantly changing. For some suchapplications, in this manner, the frictional force that is exerted uponthe axial shaft by the bearings is spread over a larger area of theaxial shaft than if the axial shaft were not to move relative to thebearings, thereby reducing wear upon the axial shaft, ceteris paribus.Alternatively or additionally, by moving in the back-and-forth motionwith respect to the bearing, the axial shaft cleans the interfacebetween the axial shaft and the bearings from any residues, such asblood residues.

For some applications, when frame 34 and impeller 50 are innon-radially-constrained configurations thereof (e.g., when the frameand the impeller are deployed within the left ventricle), the length ofthe frame exceeds the length of the impeller by at least 2 mm (e.g., atleast 4 mm, or at least 8 mm). Typically, the proximal bearing 116 anddistal bearing 118 are each 2-4 mm in length. Further typically, theimpeller and the axial shaft are configured to move axially within theframe in the back-and-forth motion at least along the length of each ofthe proximal and distal bearings, or at least along twice the length ofeach of the bearings. Thus, during the back-and-forth axial movement ofthe axial shaft, the axial shaft is wiped clean on either side of eachof the bearings.

Reference is again made to FIGS. 6A and 6B, and reference is also madeto FIG. 6C, which is a schematic illustration of anaxial-shaft-receiving tube 126 and a distal tip portion 120 ofventricular assist device 20, in accordance with some applications ofthe present invention. For some applications, the distal tip portion ofthe ventricular assist device is configured to be soft, such that thedistal tip portion is configured not to injure tissue of the subject,even if the distal tip portion comes into contact with the tissue (e.g.,tissue of the left ventricle). For example, the distal tip portion maybe made of silicone. For some applications, the distal tip portiondefines a lumen 122 therethrough. For some such applications, duringinsertion of the ventricular assist device into the left ventricle,guidewire 10 (FIG. 1B) is first inserted into the left ventricle, forexample, in accordance with known techniques. The distal tip portion ofthe ventricular assist device is then guided to the left ventricle byadvancing the distal tip portion over the guidewire, with the guidewiredisposed inside lumen 122. For some applications, a hemostasis valve 152is disposed at the distal end of the lumen 122 of distal tip portion120, such that the distal tip portion becomes sealed after the guidewireis retracted from lumen 122. Typically, during the insertion of theventricular assist device into the subject's ventricle, deliverycatheter 143 is placed over impeller 50 and frame 34 and maintains theimpeller and the frame in their radially-constrained configurations. Forsome applications, distal tip portion 120 extends distally from thedelivery catheter during the insertion of the delivery catheter into thesubject's ventricle. For some applications, at the proximal end of thedistal tip portion, the distal tip portion has a flared portion 124 thatacts as a stopper and prevents the delivery catheter from advancingbeyond the flared portion.

For some applications, axial-shaft-receiving tube 126 extends proximallyfrom distal tip portion 120. As described hereinabove, typically, theaxial shaft undergoes axial back-and-forth motion during the operationof impeller 50. Shaft-receiving tube 126 defines lumen 127, which isconfigured to receive the axial shaft when the axial shaft extendsbeyond distal bearing 118. For some applications, the shaft-receivingtube defines a stopper 128 at its distal end, the stopper beingconfigured to prevent advancement of the axial shaft beyond the stopper.For some applications, the stopper comprises a rigid component that isinserted (e.g., embedded into the distal end of the shaft-receivingtube. Alternatively, the stopper comprises a shoulder between lumen 127of the axial-shaft-receiving tube and lumen 122 of tip portion 120.Typically, such a shoulder is present since lumen 122 of tip portion 120is narrower than lumen 127. (This is because lumen 127 is typicallyconfigured to accommodate the axial shaft, while lumen 122 is configuredto accommodate guidewire 10, and the axial shaft is typically wider thanguidewire 10, since the axial shaft is itself configured to accommodateguidewire 10 within internal lumen 132 (shown in FIGS. 10B and 10C) ofthe axial shaft). Typically, during normal operation of the impeller,the axial shaft does not extend to stopper 128, even when drive cable130 (shown in FIG. 7 ) is maximally elongated. However, stopper 128 isconfigured to prevent the axial shaft from protruding into the tipportion when the delivery catheter is advanced over impeller 50 andframe 34, during retraction of ventricular assist device 20 from thesubject's ventricle. In some cases, during the advancement of thedelivery catheter over the frame and the impeller, the drive cable is atrisk of snapping. In the absence of stopper 128, in such cases the axialshaft may protrude into the tip portion. Stopper 128 prevents this fromhappening, even in the event that the drive cable snaps.

Typically, during operation of the ventricular assist device, andthroughout the back-and-forth axial motion cycle of the impeller, theimpeller is disposed in relatively close proximity to the distal tipportion. For example, the distance of the impeller to the distal tipportion may be within the distal-most 50 percent, e.g., the distal-most30 percent (or the distal-most 20 percent) of tube 24, throughout theback-and-forth motion axial cycle of the impeller.

For some applications (not shown), a portion of frame 34 extends into aproximal portion of distal tip portion 120. The portion of the frame isconfigured to cause the proximal portion of the tip to undergo radialexpansion upon being deployed within the subject's left ventricle, bythe portion of the frame being shape set to a radially-expandedconfiguration. For some applications, the entire tip portion is made ofa material having a uniform stiffness, but a portion of the frame 34that extends into the proximal portion of the tip portion impartsrigidity to the proximal portion of the tip portion, such that theproximal portion of the tip portion has a greater rigidity than thedistal portion of the tip portion.

For some applications, the tip portion has a different configuration tothat shown in FIG. 6C, as described in further detail hereinbelow, forexample, with reference to FIGS. 18-24B. For some applications, thedistal tip portion combines certain features described with respect toFIG. 6C with features described hereinbelow, for example, with referenceto FIG. 13 and to FIGS. 18-24B. For example, the internal structure ofthe tip portion and the proximal extension of axial-shaft-receiving tube126 from the tip portion may be as described with reference to FIG. 6and/or FIG. 13 , and the external shape of the tip portion may be asdescribed with reference to any one of FIGS. 18-24B.

Reference is now made to FIG. 7 , which is a schematic illustration ofan exploded view of motor unit 23 of ventricular assist device 20, inaccordance with some applications of the present invention. For someapplications, computer processor 25 of control console 21 (FIG. 1A) thatcontrols the rotation of impeller 50 is also configured to control theback-and-forth motion of the axial shaft. Typically, both types ofmotion are generated using motor unit 23. The scope of the presentinvention includes controlling the back-and-forth motion at anyfrequency. For some applications, an indication of the subject's cardiaccycle is detected (e.g., by detecting the subject's ECG), and theback-and-forth motion of the axial shaft is synchronized to thesubject's cardiac cycle.

Typically, motor unit 23 includes a motor 74 that is configured toimpart rotational motion to impeller 50, via drive cable 130. Asdescribed in further detail hereinbelow, typically, the motor ismagnetically coupled to the drive cable. For some applications, an axialmotion driver 76 is configured to drive the motor to move in an axialback-and-forth motion, as indicated by double-headed arrow 79.Typically, by virtue of the magnetic coupling of the motor to the drivecable, the motor imparts the back-and-forth motion to the drive cable,which it turn imparts this motion to the impeller. As describedhereinbelow, for some applications, the drive cable, the impeller,and/or the axial shaft undergo axial back-and-forth motion in a passivemanner, e.g., due to cyclical changes in the pressure gradient againstwhich the impeller is pumping blood. Typically, for such applications,motor unit 23 does not include axial motion driver 76.

For some applications, the magnetic coupling of the motor to the drivecable is as shown in FIG. 7 . As shown in FIG. 7 , a set of drivingmagnets 77 are coupled to the motor via a driving magnet housing 78. Forsome applications, the driving magnet housing includes ring 81 (e.g., asteel ring), and the driving magnets are adhered to an inner surface ofthe ring. For some applications, a spacer 85 is adhered to the innersurface of ring 81, between the two driving magnets, as shown. A drivenmagnet 82 is disposed between the driving magnets such that there isaxial overlap between the driving magnets and the driven magnet, and iscoupled to the proximal end of drive cable 130. For example, the drivenmagnet may be cylindrical and define a hole therethrough, and theproximal end of the drive cable may be adhered to an inner surface ofthe driven magnet that defines the hole. For some applications, thedriven magnet is cylindrical, and the magnet includes a North pole and aSouth pole, which are divided from each other along the length of thecylinder along a line 83 that bisects the cylinder, as shown. For someapplications, the driven magnet is housed inside a cylindrical housing87.

Magnetic coupling is strongest when the field density is maximizedTherefore, it is desirable to use relatively strong magnets for thedriving magnets and the driven magnet, to have a small air gap betweenthe driving magnets and the driven magnet, and to try to minimize fieldline leakage. Typically, the driving magnets and the driven magnet areneodymium magnets, which are relatively strong. Further typically, thegap between each of the driving magnets and the driven magnet is lessthan 2 mm, e.g., approximately 1 mm. In order to reduce field lineleakage, typically fewer than 4 magnets (e.g., exactly two magnets, asshown) are used as the driving magnets, for the following reason.

Typically, it is desirable to minimize the diameter of the drivenmagnet, for example, in order to stabilize the driven magnet. Asdescribed hereinabove, the driven magnet is cylindrical, and the magnetincludes a North pole and a South pole, which are divided from eachother along the length of the cylinder along dividing line 83. In theregion of the circumference of the driven magnet that is closest to thedividing line between the North and South poles of the magnet, themagnetic field lines pass directly from the North of the magnet to theSouth rather than crossing the air gap to the first outer magnet,passing through the outer magnet, around ring 81, and across the seconddriving magnet back to the South pole of the driven magnet. As anapproximation, any field line which can be drawn between the North poleand the South pole, the length of which is less than at least the totalsum of the air gaps between the driven magnet and the driving magnetswill pass from the North pole of the driven magnet to the South pole ofthe driven magnet rather than taking the alternative route. Assumingthat this adds up to all field lines extending around 2 mm of thecircumference of the driven magnet on either side of the dividing linebetween the North and South poles of the driven magnet, that is a totalof 4 mm out of the total circumference of the driven magnet that doesnot contribute toward the magnetic coupling between the driving magnetsand the driven magnet. If instead of just two poles, the driven magnethad four poles, and correspondingly there were four driving magnets,then there would be 2-mm-long wasted circumference sections four timesthroughout the circumference, which would result in a total of 8 mm outof 12 mm of the circumference of the inner magnet with wasted fieldlines. Some of this loss would be compensated by the addition of twoextra driving magnets, which add to the field strength. However, theadditional outer magnets would be relatively close to each other, whichwould result in magnetic field leaking between the driving magnets. Inview of the above, typically, the motor unit includes fewer than 4magnets (e.g., exactly two magnets, as shown) as driving magnets, andthe driven magnet is divided into fewer than four poles (e.g., exactlytwo poles, as shown).

It is noted that in the application shown in FIG. 7 , the drivingmagnets are disposed outside the driven magnet. However, the scope ofthe present application includes reversing the configurations of thedriving magnets and the driven magnet, mutatis mutandis. For example,the proximal end of the drive cable may be coupled to two or more drivenmagnets, which are disposed around a driving magnet, such that there isaxial overlap between the driven magnets and the driving magnet. Theabove discussion regarding the number of magnets that should be used asthe outer magnets, and the number of poles into which the inner magnetshould be divided, is equally applicable to such a configuration.Namely, that for such a configuration, typically, the motor unitincludes fewer than 4 magnets (e.g., exactly two magnets, as shown) asdriven magnets, and the driving magnet is divided into fewer than fourpoles (e.g., exactly two poles, as shown).

As described hereinabove, typically purging system 29 (shown in FIG. 1A)is used with ventricular assist device 20. Typically, motor unit 23includes an inlet port 86 and an outlet port 88, for use with thepurging system. For some applications, a purging fluid is continuouslyor periodically pumped into the ventricular assist device via inlet port86 and out of the ventricular assist device via outlet port 88. For someapplications, the purging fluid is pumped into the ventricular assistdevice and the inlet and outlet ports are placed in fluid communicationwith each other, such that a given volume of purging fluid circulateswithin the device for a period of time. Additional aspects of thepurging system are described hereinbelow.

Reference is now made to FIGS. 8A and 8B, which are schematicillustrations of motor unit 23, in accordance with some applications ofthe present invention. In general, motor unit 23 as shown in FIGS. 8Aand 8B is similar to that shown in FIG. 7 , and unless describedotherwise, motor unit 23 as shown in FIGS. 8A and 8B contains similarcomponents to motor unit 23 as shown in FIG. 7 . For some applications,the motor unit includes a heat sink 90 that is configured to dissipateheat that is generated by the motor. Alternatively or additionally, themotor unit includes ventilation ports 93 that are configured tofacilitate the dissipation of heat that is generated by the motor. Forsome applications, the motor unit includes vibration dampeners 94 and 96that are configured to dampen vibration of the motor unit that is causedby rotational motion and/or axial back-and-forth motion of components ofthe ventricular assist device.

For some applications, impeller 50 and axial shaft 92 are configured tomove axially back-and-forth within frame 34 in response to forces thatact upon the impeller, and without requiring the axial shaft to beactively driven to move in the axial back-and-forth motion. Typically,over the course of the subject's cardiac cycle, the pressure differencebetween the left ventricle and the aorta varies from being approximatelyzero during ventricular systole (hereinafter “systole”) to a relativelylarge pressure difference (e.g., 60-100 mmHg) during ventriculardiastole (hereinafter “diastole”). For some applications, due to theincreased pressure difference that the impeller is pumping againstduring diastole, the impeller is pushed distally with respect to frame34 during diastole, relative to the location of the impeller withrespect to frame 34 during systole. In turn, since the impeller isconnected to the axial shaft, the axial shaft is moved forward. Duringsystole, the impeller (and, in turn, the axial shaft) move back to theirsystolic positions. In this manner, the axial back-and-forth motion ofthe impeller and the axial shaft is generated in a passive manner, i.e.,without requiring active driving of the axial shaft and the impeller, inorder to cause them to undergo this motion.

Reference is now made to FIG. 9 , which is a graph indicating variationsin the length of a drive cable of a ventricular assist device, as apressure gradient against which the impeller of the ventricular assistdevice varies, as measured in experiments performed by inventors of thepresent application. An impeller and a drive cable as described hereinwere used to pump a glycerin-based solution through chambers, with thechambers set up to replicate the left ventricle and the aorta, and thesolution having properties (such as, density and viscosity) similar tothose of blood. The pressure gradient against which the impeller waspumping varied, due to an increasing volume of fluid being disposedwithin the chamber into which the impeller was pumping. At the sametime, movement of the drive cable was imaged and changes in the lengthof the drive cable were determined via machine-vision analysis of theimages. The graph shown in FIG. 9 indicates the changes in the length ofthe drive cable that were measured, as a function of the pressuregradient. The y-axis of the graph shown in FIG. 9 is such that 0 mmelongation represents the length of the drive cable when the impeller isat rest. It is noted that the graph starts at a pressure gradient valueof 65 mmHg, and that at this pressure the elongation is negative (atapproximately −0.25 mm), i.e., the drive cable is shortened relative tothe length of the drive cable prior to initiation of rotation of theimpeller. This is because the drive cable was configured such that, whenthe impeller first started pumping, the drive cable shortened (relativeto the length of the drive cable before the impeller was activated), dueto coils within the drive cable unwinding, as described in furtherdetail hereinbelow. As seen in the section of the curve that is shown inFIG. 9 , after the initial shortening of the drive cable that resultedfrom the aforementioned effect, it was then the case that as thepressure gradient increased, the drive cable became increasinglyelongated.

As indicated by the results shown in FIG. 9 and as describedhereinabove, it is typically the case that, in response to variations inthe pressure against which the impeller is pumping blood (e.g., thepressure difference between the left ventricle and the aorta), theimpeller moves back and forth with respect to frame 34. In turn, themovement of the impeller causes drive cable 130 to become more or lesselongated.

For some applications, during operation of the ventricular assistdevice, computer processor 25 of control console 21 (FIG. 1A) isconfigured to measure an indication of the pressure exerted upon theimpeller (which is indicative of the pressure difference between theleft ventricle and the aorta), by measuring an indication of tension indrive cable 130, and/or axial motion of the drive cable. For someapplications, based upon the measured indication, the computer processordetects events in the subject's cardiac cycle, determines the subject'sleft-ventricular pressure, and/or determines the subject's cardiacafterload. For some applications, the computer processor controls therotation of the impeller, and/or the axial back-and-forth motion of theaxial shaft in response thereto.

For some applications, generally similar techniques are applied to aright ventricular assist device that is configured to pump blood fromthe right ventricle to the pulmonary artery, and the computer processoris configured to determine the pressure difference between the rightventricle and the pulmonary artery in a generally similar manner,mutatis mutandis. For some applications, generally similar techniquesare applied to a cardiac assist device that is configured to pump bloodfrom a first location to a second location (such as, from the vena cavato the right ventricle, from the right atrium to the right ventricle,from the vena cava to the pulmonary artery, and/or from right atrium tothe pulmonary artery), and the computer processor is configured todetermine the pressure difference between the first location and thesecond location in a generally similar manner, mutatis mutandis.

Referring again to FIG. 7 , for some applications, ventricular assistdevice 20 includes a sensor 84. For example, the sensor may include aHall sensor that is disposed within motor unit 23, as shown in FIG. 7 .For some applications, the Hall sensor measures variations in themagnetic field that is generated by one of the magnets in order tomeasure the axial motion of drive cable 130, and, in turn, to determinethe pressure against which the impeller is pumping. For example, theinner, driven magnet 82 may be axially longer than the outer, drivingmagnets 77. Due to the inner magnet being longer than the outer magnets,there are magnetic field lines that emanate from the inner magnet thatdo not pass to the outer magnets, and the magnetic flux generated bythose field lines, as measured by the Hall sensor, varies as the drivecable, and, in turn, the inner magnet moves axially. During operation,motor 74 rotates, creating an AC signal in the Hall sensor, whichtypically has a frequency of between 200 Hz and 800 Hz. Typically, asthe tension in the drive cable changes due to the subject's cardiaccycle, this gives rise to a low frequency envelope in the signalmeasured by the Hall sensor, the low frequency envelope typically havinga frequency of 0.5-2 Hz. For some applications, the computer processormeasures the low frequency envelope, and derives the subject's cardiaccycle from the measured envelope. It is noted that typically the axialmotion of the magnet is substantially less than that of the impeller,since the full range of motion of the impeller isn't transmitted alongthe length of the drive cable. However, it is typically the case thatthe axial back-and-forth motion of the impeller gives rise to ameasurable back-and-forth motion of the magnet.

For some applications, the Hall sensor measurements are initiallycalibrated, such that the change in magnetic flux per unit change inpressure against which the impeller is pumping (i.e., per unit change inthe pressure difference between the left ventricle and the aorta) isknown. It is known that, in most subjects, at systole, theleft-ventricular pressure is equal to the aortic pressure. Therefore,for some applications, the subject's aortic pressure is measured, andthe subject's left-ventricular pressure at a given time is thencalculated by the computer processor, based upon (a) the measured aorticpressure, and (b) the difference between the magnetic flux measured bythe Hall sensor at that time, and the magnetic flux measured by the Hallsensor during systole (when the pressure in the left ventricle isassumed to be equal to that of the aorta).

Reference is now made to FIGS. 10A, 10B, and 10C, which are schematicillustrations of drive cable 130 of ventricular assist device 20, inaccordance with some applications of the present invention. Typically,the rotational motion of the impeller (which is imparted via the axialshaft), as well as the axial back-and-forth motion of the axial shaftdescribed hereinabove, is imparted to the axial shaft via the drivecable, as described hereinabove. Typically, the drive cable extends frommotor unit 23 (which is typically disposed outside the subject's body)to the proximal end of axial shaft 92 (as shown in FIG. 10C, which showsthe connection between the distal end of the drive cable and theproximal end of the axial shaft). For some applications, the drive cableincludes a plurality of wires 134 that are disposed in a tightly-coiledconfiguration in order to impart sufficient strength and flexibility tothe drive cable, such that a portion of the cable is able to bemaintained within the aortic arch (the portion corresponding to arrow145 in FIG. 10A), while the cable is rotating and moving in the axialback-and-forth motion. The drive cable is typically disposed within afirst outer tube 140, which is configured to remain stationary while thedrive cable undergoes rotational and/or axial back-and-forth motion. Thefirst outer tube is configured to effectively act as a bearing along thelength of the drive cable. Typically, the first outer tube is made of apolymer (such as, polyether ether ketone) that is configured to behighly resistant to fatigue even under the frictional forces that aregenerated by the relative motion between the drive cable and the firstouter tube. However, since such polymers are typically relatively rigid,only a thin layer of the polymer is typically used in the first outertube. For some applications, the first outer tube is disposed within asecond outer tube 142, which is made of a material having greaterflexibility than that of the first outer tube (e.g., nylon, and/orpolyether block amide), and the thickness of the second outer tube isgreater than that of the first outer tube.

Typically, during insertion of the impeller and the cage into the leftventricle, impeller 50 and frame 34 are maintained in aradially-constrained configuration by delivery catheter 143. Asdescribed hereinabove, in order for the impeller and the frame to assumenon-radially-constrained configurations, the delivery catheter isretracted. For some applications, as shown in FIG. 10A, the deliverycatheter remains in the subject's aorta during operation of the leftventricular device, and outer tube 142 is disposed inside the deliverycatheter. In order to retract the left ventricular device from thesubject's body, the delivery catheter is advanced over the impeller andthe frame, such that the impeller and the frame assume theirradially-constrained configurations. The catheter is then withdrawn fromthe subject's body.

Referring to FIG. 10C, typically, the axial shaft and the cable define acontinuous lumen 132 therethrough. For some applications, the leftventricular device is guided to the aorta and to the left ventricle byplacing the axial shaft and the cable over guidewire 10 (describedhereinabove), such that the guidewire is disposed inside lumen 132. Forsome applications, by using the lumen of the axial shaft and the cablein this manner, it is not necessary to provide an additional guidewireguide to be used during insertion of left ventricular assist device 20.For some applications, the axial shaft and the cable each have outerdiameters of more than 0.6 mm (e.g., more than 0.8 mm), and/or less than1.2 mm (e.g., less than 1 mm), e.g., 0.6-1.2 mm, or 0.8-1 mm. For someapplications, the diameter of lumen 132, defined by the shaft and thecable, is more than 0.3 mm (e.g., more than 0.4 mm), and/or less than0.7 mm (e.g., less than 0.6 mm), e.g., 0.3-0.7 mm, or 0.4-0.6 mm. Forsome applications, drive cable 130 has a total length of more than 1 m(e.g., more than 1.1 m), and/or less than 1.4 m (e.g., less than 1.3 m),e.g., 1-1.4 m, or 1.1-1.3 m. As described hereinabove, for someapplications, the guidewire additionally passes through lumen 122 ofdistal tip portion 120. Typically, the diameter of lumen 122 isgenerally similar to that of lumen 132.

Referring to FIG. 10B, for some applications, drive cable 130 is made upof a plurality of coiled wires 134. Typically, due to the impellerhaving to pump against a pressure gradient during diastole, the impelleris pushed distally with respect to frame 34, relative to the position ofthe impeller with respect to the frame during systole, as describedhereinabove. If the direction of rotation of the impeller is such thatrotation of the drive cable in this direction results in the coiledwires of the drive cable at least partially tightening, then this wouldalso cause the impeller to advance with respect to the frame when therotation of the impeller is initiated, due to the coiled wirestightening (i.e., becoming wound up such that the radius of the coildecreases), and thereby axially elongating. For some applications, atleast a portion of the drive cable is configured such that (a) inresponse to the impeller pumping blood from the left ventricle to theaorta, by rotating in a predefined direction of rotation, (b) rotationof the drive cable in this direction results in the coiled wires of thedrive cable along the portion of the drive cable at least partiallyunwinding, such that the portion of the drive cable axially shortens. Byconfiguring the drive cable in the aforementioned manner, the length offrame 34 does not need to accommodate distal movement of the impellerresulting from the drive cable axially elongating, in addition toaccommodating the distal movement of the impeller within the frameresulting from the changes in pressure due to the subject's cardiaccycle (as described hereinabove). For some applications, the extent towhich the drive cable is able to unwind and thereby axially shorten islimited by the outer tube in which the drive cable is disposedpreventing the drive cable from radially expanding. Therefore, for someapplications, the axial shortening of the drive cable is by a relativelysmall amount. For some applications, due to the outer tube limiting theextent to which the drive cable is able to unwind and thereby axiallyshorten, the drive cable doesn't shorten. However, even in suchapplications, the drive cable is typically configured not to elongate,due to the windings of the coil being configured as describedhereinabove.

Alternatively or additionally, the impeller is inserted into frame 34,such that the drive cable is already in a preloaded state (i.e., suchthat the impeller exerts tension on the drive cable that causes thedrive cable to be axially elongated relative to its rest state). Due tothe preloading of the drive cable, when the rotation of the impeller isinitiated, this does not cause the drive cable to axially elongate,since the drive cable is already in an axially elongated state relativeto its rest state. For some such applications, the impeller is stillconfigured to undergo axial back-and-forth motion as a result of changesin pressure due to the subject's cardiac cycle (as describedhereinabove).

For some applications, debris is generated by frictional forces betweenthe drive cable and outer tube 140. Alternatively or additionally, afluid (e.g., purging fluid) is disposed between the drive cable and theouter tube. Typically, due to the windings of the coiled drive cable,the drive cable acts as an impeller and pumps the debris and/or thefluid axially with respect to outer tube 140. For some applications, thedirection of the windings of the drive cable is such that the drivecable is configured, by rotating in a predefined rotation direction, topump the debris and/or the fluid toward a proximal end of theventricular assist device, and not to pump the debris and/or the fluidtoward the distal end of the ventricular assist device toward thepatient's left ventricle.

Reference is now made to FIGS. 11A and 11B, which are schematicillustrations of an interface component 154 that forms an interfacebetween respective portions of drive cable 130 of ventricular assistdevice 20, in accordance with some applications of the presentinvention. For some applications, the drive cable includes first andsecond portions. Reference is also again made to FIG. 10A, typically,the first portion is configured to be disposed in the subject's aorticarch (i.e., the portion of the aorta corresponding to arrow 145), andthe second portion is configured to be disposed along the descendingaorta (the portion of the aorta corresponding to arrow 147), andtypically to extend until motor unit 23, outside the subject's body.Typically, at locations at which drive cable 130 undergoes substantialcurvature, such as the aortic arch, it is desirable for the drive cableto be relatively flexible. However, a drive cable having greaterflexibility is typically also more axially stretchable than a drivecable having less flexibility. Therefore, for some applications, thereis a tradeoff between wanting the drive cable being flexible enough toconform to the curvature of the aortic arch, but on the other hand notwanting the drive cable to undergo substantial axial stretching (whichmay result in a loss of control over the axial positions of theimpeller). For some applications, the respective portions of the drivecable have respective levels of flexibility. For example, the firstportion of the drive cable that is configured to be disposed in theaortic arch may have a first flexibility, while the second portion ofthe drive cable that is configured to be disposed in the descendingaorta may have a second flexibility, the first flexibility being greaterthan the second flexibility.

For some applications, the first portion is configured to have greaterflexibility than the second portion, by the coil of wires 134 in thefirst portion including fewer wires than in the second portion. Forexample, as shown in FIGS. 11A-B, the first portion may include morethan 4 wires and fewer than 8 wires (e.g., 4-8 wires, or 5-7 wires,e.g., 6 wires), and the second portion may include more than 8 wires andfewer than 12 wires (e.g., 8-12 wires, or 9-11 wires, e.g., 10 wires).For some applications, the length of the first portion of the drivecable is more than 20 cm (e.g., more than 25 cm) and less than 40 cm(e.g., less than 35 cm), e.g., 20-40 cm, or 25-35 cm. For someapplications, the length of the second portion of the drive cable ismore than 60 cm (e.g., more than 70 cm) and less than 100 cm (e.g., lessthan 90 cm), e.g., 60-100 cm, or 70-90 cm.

For some applications, the two portions of the drive cable are coupledto each other via interface component 154. Typically, the wires of thetwo portions are welded to the interface component. For someapplications, grooves 157 are cut into the interface component. Thegrooves are configured such that stress generated by a wire at theinterface is spread over the radius of the groove as opposed to beingconcentrated at the point at which the wire is welded to the interfacecomponent. For some such applications, the interface componentadditionally includes protrusions 158 that hold the wires in placeduring welding of the wires to the interface component.

Reference is now made to FIGS. 11C, 11D, and 11E, which are schematicillustrations of an interface 156 between the drive cable and axialshaft 92 of the ventricular assist device, in accordance with someapplications of the present invention. For some applications, generallysimilar techniques to those described with reference to FIGS. 11A-B areused to couple the drive cable to the axial shaft. For someapplications, the proximal end of the axial shaft (which definesinterface 156) includes grooves 157 and/or protrusions 158, which aregenerally as described hereinabove, and which are shown in FIG. 11C.

Referring to FIG. 11D, for some applications, as the coiled wiresapproach interface 156, the coiled wires are at least partiallystraightened (i.e., the pitch of the wires is increased), such that theangle that the wires make with the interface is less acute than it wouldbe if the wire were not straightened. By making the angle less acute,stress at the point at which the wires are welded to the interfacecomponent is reduced. Referring to FIG. 11E, for some applications, asthe wires approach interface 156, in addition to being straightened, thewires are flattened and pushed radially inward. For some applications,the wires are sufficiently flattened that each of the wires in the coilcome into contact with adjacent wires thereto, such as to form acylinder, as shown. For example, the shapes of the wires may be changedfrom having a circular cross-section with a radius of approximately 0.2mm to an elliptical cross-section having a minor axis of 0.12 mm. Forsome applications, the flattening is performed along a length of between1 mm and 3 mm. For some applications, the wires are flattened by placingan overtube 159 around the wires, placing the overtube and the wires ona mandrel, and squeezing the overtube and the wires radially inward.Subsequently, the overtube and the flattened wires are welded to axialshaft 92 at the interface.

For some applications, generally similar techniques to those describedwith reference to FIGS. 11D and 11E are used for coupling the twoportions of the drive cable to each other. For some applications, as thecoiled wires approach interface component 154, the coiled wires are atleast partially straightened (i.e., the pitch of the wires isincreased), such that the angle that the wires make with the interfaceis less acute than it would be if the wires were not straightened. Bymaking the angle less acute, stress at the point at which the wires arewelded to the interface component is reduced. For some applications, asthe wires approach interface component 154, in addition to beingstraightened, the wires are flattened and pushed radially inward. Forsome applications, the wires are sufficiently flattened that each of thewires in the coil come into contact with adjacent wires thereto, such asto form a cylinder. For example, the shapes of the wires may be changesfrom having a circular cross-section with a radius of approximately 0.2mm to an elliptical cross-section having a minor axis of 0.12 mm. Forsome applications, the flattening is performed along a length of between1 mm and 3 mm. For some applications, the wires are flattened by placingan overtube (not shown, but similar to overtube 159) around the wires,placing the overtube and the wires on a mandrel, and squeezing theovertube and the wires radially inward. Subsequently, the overtube andthe flattened wires are welded to interface component 154.

For some applications, swaging techniques are used for coupling the twoportions of the drive cable to each other. For some such applications,the ends of inner and outer tubes are placed respectively inside andoutside of the ends of the two portions of the drive cable that willform the interface between the portions. The inner tube is then placedover a rigid mandrel and the inner and outer tubes and the ends of thedrive cable are swaged together by applying pressure around the outsideof the outer tube. Once the ends of the portions of the drive cable, aswell as the inner and outer tubes, have been swaged together, this formsthe interface between the portions of the drive cable. For someapplications, similar swaging techniques are performed for coupling thedrive cable to the axial shaft at interface 156.

Reference is now made to FIG. 12 , which is a schematic illustration ofdrive cable 130 of ventricular assist device 20 that includesfriction-reduction elements 170 disposed around at least a portion ofthe drive cable, in accordance with some applications of the presentinvention. For some applications, friction-reduction elements 170 areused to reduce friction between drive cable 130 (which rotates duringthe operation of the ventricular assist device) and outer tube 142(which remains stationary during the rotation of the drive cable). Inthe example shown, friction-reduction elements 170 are ball bearings.However, the scope of the present invention includes using otherfriction-reduction elements to reduce friction between the drive cableand the outer tube. For example, other rolling-element bearings may beused, such as cylindrical rollers, spherical rollers, gear bearings,tapered rollers, needle rollers, and/or toroidal roller bearings. Forsome applications, friction-reduction elements are used as analternative to including first outer tube 140 in addition to secondouter tube 142. In the example shown in FIG. 12 , the friction-reductionelements are disposed between the drive cable and the second outer tube,and the ventricular assist device does not include first and secondouter tubes.

Typically, the ventricular assist device traverses the subject's aorticarch, and/or other portions of the subject's vasculature that aresubstantially curved. In the absence of the friction-reduction elements,drive cable 130 and tube 142 would typically contact each other,particularly at the curved portions of the vasculature. As describedhereinabove, drive cable 130 typically undergoes rotational motion, andfor some applications additionally undergoes back-and-forth axialmotion, with respect to tube 142. Therefore, in the absence of thefriction-reduction elements (or first outer tube 140, as describedhereinabove), there would be substantial frictional forces generated atthe locations at which the drive cable and outer tube 142 are in contactwith each other. Therefore, for some applications, thefriction-reduction elements are disposed between drive cable 130 andouter tube 142, in order to reduce frictional forces generated at thelocations at which drive cable 130 and outer tube 142 are in contactwith each other. For some applications, the friction-reduction elementsare disposed between drive cable 130 and outer tube 142 substantiallyalong the full length of drive cable 130 and outer tube 142.Alternatively, the friction-reduction elements are disposed betweendrive cable 130 and outer tube 142 at locations at which drive cable 130and outer tube 142 are configured to be substantially curved, e.g., atthe location at which drive cable 130 and outer tube 142 are disposedwithin the aortic arch, during operation of the ventricular assistdevice.

Reference is now made to FIG. 13 , which is a schematic illustration ofa procedure for purging drive cable 130 of ventricular assist device 20,in accordance with some applications of the present invention. For someapplications, proximal to proximal bearing 116, axial shaft 92 and cable130 are surrounded by first and second outer tubes 140 and 142, asdescribed hereinabove. Typically, both the first and second outer tubesremain stationary, during rotation of the drive cable. For someapplications, a purging fluid (e.g., a fluid containing glucose ordextrose) is pumped between the first and second outer tubes, and thereis an opening 146 within the first outer tube in the vicinity of theproximal bearing. As described hereinabove, typically purging system 29(shown in FIG. 1A) controls the flow of the purging fluid via inlet port86 and outlet port 88 (shown in FIGS. 7, 8A, and 8B). For someapplications, the purging fluid flows between drive cable 130, and firstouter tube 140, as indicated by purging-fluid-flow arrow 148 in FIG. 13. In this manner, the interface between drive cable 130 (which rotates),and outer tube 140 (which remains stationary, during rotation of thedrive cable) is purged. For some applications, some of the purging fluidadditionally flows to the interface between the axial shaft and proximalbearing 116, thereby purging the interface, as indicated bypurging-fluid-flow arrow 149 in FIG. 13 .

For some applications, purging fluid is pumped through lumen 132 definedby drive cable 130 and axial shaft 92, such that at least some fluidflows all the way to the distal end of the axial shaft. For someapplications, in this manner, some of the purging fluid flows to theinterface between the axial shaft and distal bearing 118, therebypurging the interface, as indicated by purging-fluid-flow arrow 150 inFIG. 13 .

For some applications, hemostasis valve 152 is disposed at the distalend of the lumen 122 of distal tip portion 120, as describedhereinabove. Alternatively or additionally, a plug (not shown) isdisposed at the distal end of the lumen 122 of tip portion 120.Typically, the hemostasis valve and/or the plug prevents blood fromflowing into lumen 122, and/or into lumen 132. Further typically, theplug, by preventing purging fluid from flowing out of the distal end oflumen 122, causes the purging fluid to flow toward the interface betweenaxial shaft 92 and distal bearing 118, as indicated bypurging-fluid-flow arrow 150 in FIG. 13 .

For some applications, alternative techniques to those describedhereinabove are used for introducing fluid (e.g., a fluid containingglucose) to the ventricular assist device. In the application shown inFIG. 13 , fluid is allowed to flow distally after passing throughopening 146, as indicated by arrow 149, and as described hereinabove.However, for some applications, flow of the fluid in the distaldirection is blocked (i.e., the flow of fluid indicated by arrow 149 isabsent). For some such applications, fluid is initially released intothe space between drive cable 130 (which rotates), and outer tube 140(which remains stationary, during rotation of the drive cable), suchthat the fluid fills the space between the drive cable and outer tube140, proximal to opening 146. For example, the fluid may be pumped intothe space via the gap between first outer tube 140 and second outer tube142, as shown. The fluid is then kept in place, between the drive cableand outer tube 140, proximal to opening 146, typically, throughout theoperation of the ventricular assist device. The fluid is configured toremove air from the space between the drive cable and the outer tube,and/or to reduce frictional forces between drive cable 130 (whichrotates), and outer tube 140 (which remains stationary, during rotationof the drive cable).

For some applications, a generally similar technique is performed, butthe fluid is pumped between the drive cable 130 (which rotates), andouter tube 140 (which remains stationary, during rotation of the drivecable), during operation of the ventricular assist device. For example,the fluid may be pumped into the space via the gap between first outertube 140 and second outer tube 142, as shown. For some applications, thefluid is continuously pumped between the drive cable and the outer tube,during operation of the ventricular assist device, or is periodicallypumped between the drive cable and the outer tube during operation ofthe ventricular assist device. It is noted that even for suchapplications, the fluid is pumped between the drive cable and the outertube, but does not flow into the subject's bloodstream, since flow ofthe fluid in the distal direction is blocked, as described hereinabove.The pumping of the fluid is configured to remove air from the spacebetween the drive cable and the outer tube, to reduce frictional forcesbetween drive cable 130 (which rotates) and outer tube 140 (whichremains stationary, during rotation of the drive cable), and/or toremove debris generated by the ventricular assist device from theinterface between the drive cable and the outer tube.

Reference is now made to FIGS. 14A and 14B, which are schematicillustrations of frame 34 of ventricular assist device 20, a stator 182being coupled to a proximal portion of the frame, in accordance withsome applications of the present invention. For some applications, thestator is integrally formed with frame 34, as described in furtherdetail hereinbelow. Typically, the stator includes a plurality of curvedprojections 66 (e.g., more than 2, and/or less than 8 curved projections66) that, when device 20 is in a non-radially-constrained configuration,extend from frame 34, and that are made of a flexible material, e.g., apolymer, such as polyurethane, and/or silicone. The curvature of thecurved projection is typically such as to oppose the direction ofrotation of the impeller, as described in further detail hereinbelow.For some applications, by virtue of using projections that are curved(e.g., curved such as to oppose the direction of rotation of theimpeller of the ventricular assist device as described in further detailhereinbelow), stator 182 is configured to reduce rotational flowcomponents from the blood flow prior to the blood flowing from theproximal end of the frame of the ventricular assist device.

As described hereinabove, typically, device 20 is inserted into thesubject's ventricle transcatheterally, while frame 34 is in aradially-constrained state. Upon being released from the catheter, theframe automatically assumes its non-constrained shape, due to frame 34self-expanding. Typically, during the insertion of the frame to the leftventricle, the curved projections of the stator are in folded states,and do not substantially increase the minimal diameter to which theframe can be radially-constrained, relative to if the tube did notcontain the curved projections. Upon frame 34 expanding, the curvedprojections are configured to automatically assume their curvedconfigurations, due to the curved projections being coupled to frame 34.

For some applications, curved projections 66 are made of a flexiblematerial, e.g., a polymer, such as polyurethane, and/or silicone. Thecurved projections are typically coupled to struts 186 of frame 34 thatare curved, the curvature of the curved struts thereby defining thecurvature of the curved projections. Typically, the flexible material iscoupled to frame 34, such that the flexible material defines a lumen 188(FIG. 14B) therethrough that is aligned with the longitudinal axis ofthe frame. Axial shaft 92 of the ventricular assist device typicallypasses into the proximal end of the frame via lumen 188.

For some applications, in order to facilitate the coupling of theflexible material to the frame, in order to shape the flexible materialin a desired shape, and/or in order to facilitate the formation of lumen188, a plurality of elongate elements 190 (e.g., strings and/or wires,which are typically made of a similar material to elongate elements 67)are tied to the proximal end of the frame. For some applications, curvedstruts 186 define rings 192 or other coupling elements at distal endsthereof, to which elongate elements 190 are tied. The flexible materialis typically coupled to the frame, such that curved films of materialare supported by the curved struts and the elongate elements, each ofthe films defining a respective curved projection. For someapplications, the strings and/or wires that are tied to the proximal endof the frame are tied to define a circle 191, which defines one of theends of lumen 188. For example, during the formation of the stator, amandrel may be placed through proximal bearing 116, and the elongateelements may be tied to rings 192 and made to encircle the mandrel, suchas to define the pattern of elongate elements shown in FIG. 14B. Theproximal end of the frame with the elongate elements and the mandrel isthen dipped into the material (which is typically a polymer, such assilicone), while the material is in an uncured, liquid state.Subsequently, the material is cured such that it solidifies, e.g., bybeing left to dry. Once the material has dried, the mandrel is typicallyremoved. For some applications, the other end of lumen 188 is defined byproximal bearing 116 disposed at the proximal end of frame 34.Typically, the flexible material extends from circle 191 defined by thestrings and/or wires to proximal bearing 116, such as to define lumen188. For some applications sutures 189 are tied around curved struts186, in order to facilitate coupling between the material and thestruts, e.g., as described hereinabove with reference to sutures 53 ofimpeller 50.

Reference is now made to FIG. 15A, which is a schematic illustration ofa flattened profile of frame 34 of ventricular assist device 20, inaccordance with some applications of the present invention. As shown,the frame includes curved struts 186, at its proximal end, with rings192 disposed toward the tips of each of the struts. Reference is alsomade to FIG. 15B, which is a schematic illustration showing an enlargedview of the proximal end of frame 34, in accordance with someapplications of the present invention. A tip 194 of curved strut 186typically defines the orientation of the leading edge of thecorresponding blade (i.e., curved projection) of the stator, once theflexible material is coupled to the curved strut. Reference isadditionally made to FIG. 15C, which is a schematic illustration offrame 34, showing the frame with the material that defines curvedprojections 66 coupled to the frame, in accordance with someapplications of the present invention. It may be observed that theorientations of the leading edges of the curved projections are definedby the orientations of the corresponding tips of the curved struts.

As shown in FIG. 15B, the tip 194 of curved strut 186 is shaped todefine an angle alpha with respect to the axial component of blood flowthrough the frame, which is indicated by arrow 196, and which isparallel to the longitudinal axis of the frame, and toward the proximalend of the frame. The leading edge of the corresponding curvedprojections typically also defines an angle that is approximately equalto angle alpha, with respect to the general direction of blood flow, asindicated in FIG. 15C. (For some applications, upon struts 186undergoing radial expansion, the angle of the leading edges of thecurved projections becomes slightly less than alpha.) For someapplications, angle alpha is greater than 45 degrees (e.g., greater than60 degrees), and/or less than 85 degrees (e.g., less than 80 degrees),e.g., 45-85 degrees, or 60-80 degrees.

The direction of rotation of the impeller is indicated by arrow 198 inFIG. 15C. As may be observed in FIG. 15C, the curvature of the curvedprojections is typically such as to oppose the direction of rotation ofthe impeller (which is the direction of rotation of rotational flowcomponents within the blood flow, as imparted to the blood flow by theimpeller). From the distal ends of the curved projections to theirproximal ends, the curved projections curve such as to becomeprogressively closer to being parallel with the longitudinal axis of theframe. The curvature of the curved projections is such as to reducerotational flow components from the blood flow prior to the bloodflowing from the proximal end of the frame of the ventricular assistdevice.

Reference is now made to FIGS. 16A, 16B, 16C and 16D, which areschematic illustrations of ventricular assist device 20, the ventricularassist device including one or more blood-pressure-measurement tubes210, in accordance with some applications of the present invention. Asdescribed hereinabove, typically, the ventricular assist device includestube 24, which traverses the subject's aortic valve, such that aproximal end of the tube is disposed within the subject's aorta and adistal end of the tube is disposed within the subject's left ventricle.Typically, a blood pump, which typically includes impeller 50, isdisposed within the subject's left ventricle within tube 24, and isconfigured to pump blood through tube 24 from the left ventricle intothe subject's aorta. For some applications, blood-pressure-measurementtube 210 is configured to extend to at least an outer surface 212 oftube 24, such that an opening 214 at the distal end of theblood-pressure-measurement tube is in direct fluid communication withthe patient's bloodstream outside tube 24. A pressure sensor 216(illustrated schematically in FIG. 1A) measures pressure of blood withinthe blood-pressure-measurement tube. Typically, by measuring pressure ofblood within the blood-pressure-measurement tube, the pressure sensorthereby measures the subject's blood pressure outside tube 24.Typically, blood-pressure-measurement tube 210 extends from outside thesubject's body to opening 214 at the distal end of the tube, andpressure sensor 216 is disposed toward a proximal end of the tube, e.g.,outside the subject's body. For some applications, computer processor 25(FIG. 1A), receives an indication of the measured blood pressure andcontrols the pumping of blood by the impeller, in response to themeasured blood pressure.

Referring to FIGS. 16A and 16B, for some applications, the one or moreblood-pressure-measurement tubes include one or more left ventricularblood-pressure-measurement tubes 220 that are configured to extend tothe outer surface of blood-pump tube 24 at a location along the tubethat is configured to be within the subject's left ventricle proximal tothe blood pump (e.g., proximal to impeller 50). For such applications,the pressure sensor is configured to measure the subject'sleft-ventricular pressure by measuring pressure of blood within theleft-ventricular blood-pressure-measurement tube. For some applications,the ventricular assist device includes two or more such left ventricularblood-pressure-measurement tubes, e.g., as shown in FIGS. 16A and 16B.For some applications, based upon the blood pressures measured withineach of the left ventricular blood-pressure-measurement tubes, computerprocessor 25 determines whether the opening of one of the two or moreleft-ventricular blood-pressure-measurement tubes is occluded. This mayoccur, for example, due to the opening coming into contact with the wallof the interventricular septum, and/or a different intraventricularportion. Typically, in response to determining that the opening of oneof the two or more left-ventricular blood-pressure-measurement tubes isoccluded, the computer processor determines the subject'sleft-ventricular pressure based upon the blood pressure measured withina different one of the two or more left-ventricularblood-pressure-measurement tubes.

For some applications, the one or more blood-pressure-measurement tubesinclude one or more aortic blood-pressure-measurement tubes 222 that areconfigured to extend to the outer surface of the tube at a locationalong the tube that is configured to be within the subject's aorta, asshown in FIG. 16C. For such applications, the pressure sensor isconfigured to determine the subject's aortic pressure by measuringpressure of blood within the aortic blood-pressure-measurement tube. Forsome applications, the ventricular assist device includes two or moresuch aortic blood-pressure-measurement tubes, e.g., as shown in FIG.16C. For some applications, based upon the blood pressures measuredwithin each of the aortic blood-pressure-measurement tubes, computerprocessor 25 determines whether the opening of one of the two or moreaortic blood-pressure-measurement tubes is occluded. This may occur, forexample, due to the opening coming into contact with the wall of theaorta. Typically, in response to determining that the opening of one ofthe two or more aortic blood-pressure-measurement tubes is occluded, thecomputer processor determines the subject's aortic pressure based uponthe blood pressure measured within a different one of the two or moreaortic blood-pressure-measurement tubes.

For some applications, the ventricular assist device includes both leftventricular blood-pressure-measurement tubes and aorticblood-pressure-measurement tubes all of which extend to the outersurface of tube 24, e.g., as shown in FIG. 16C.

Still referring to FIG. 16C, as described hereinabove, for someapplications, drive cable 130 extends from a motor outside the subject'sbody to axial shaft 92 upon which impeller 50 is disposed. Typically,the drive cable is disposed within outer tube 142. For someapplications, the drive cable is disposed within first outer tube 140and second outer tube 142, as described hereinabove. For someapplications, the one or more blood-pressure measurement tubes aredisposed within outer tube 142, surrounding the drive cable. For someapplications, portions of the one or more blood-pressure-measurementtubes are defined by the walls of outer tube 142, as shown. For someapplications, within outer tube 142, the blood pressure measurementtubes have elliptical cross-sections (as shown). Typically, thisincreases the cross-sectional areas of the tubes, relative to if theywere to have circular cross-sections. Typically, within a distal portionof each of the blood-pressure measurement tubes (which extends toopening 214), the tube has a circular cross-section. For someapplications, the diameter of the distal portion of the tube is morethan 0.2 mm, and/or less than 0.5 mm (e.g., 0.2-0.5 mm).

As shown in FIG. 16A, for some applications, aortic blood pressure ismeasured using at least one aortic blood-pressure-measurement tube 222that defines an opening 219 in outer tube 142 at its distal end. Theaortic blood-pressure-measurement tube is configured to extend fromoutside the subject's body to an outer surface of outer tube 142 withinthe subject's aorta, such that the opening at the distal end of theaortic blood-pressure-measurement tube is in direct fluid communicationwith the subject's aortic bloodstream. It is noted that, for suchapplications, the aortic blood-pressure-measurement tube does not extendto the outer surface of tube 24. Blood pressure sensor 216 is configuredto measure the subject's aortic blood pressure by measuring bloodpressure within the aortic blood-pressure-measurement tube. For someapplications, opening 219 in outer tube 142 is disposed within tube 24,as shown in FIG. 16D. Aortic pressure is measured via opening 219, sincepressure inside tube 24 at locations downstream of the impeller istypically equal to aortic pressure.

As shown in FIGS. 16A and 16B, for some applications, outer tube 142defines a groove 215 in a portion of the outer surface of the outer tubethat is configured to be disposed within tube 24. Typically, duringinsertion of the ventricular assist device into the subject's body, theportion of blood-pressure-measurement tube 210 that extends from withintube 24 to at least an outer surface of tube 24, is configured to bedisposed within the groove, such that the portion of theblood-pressure-measurement tube does not protrude from the outer surfaceof the outer tube.

Referring now to FIG. 16D, for some applications, distal portions ofblood-pressure-measurement tubes 210 are disposed on the outside of tube24. For example, as shown, blood-pressure-measurement tubes 210 mayextend from outer tube 142 to the proximal end of tube 24, andthereafter the blood pressure measurement tubes may be built into theouter surface of tube 24. For some applications, one or more tubes runalong the outer surface of tube 24 in the manner shown in FIG. 16D, butthe tubes continue until the distal end of tube 24 until tip portion 120of the ventricular assist device. The tubes are used to inflate aninflatable portion of the tip portion as described in further detailhereinbelow with reference to FIG. 21C.

Although the ventricular assist device as described with reference toFIGS. 16A-D has been described as including a blood pump that isconfigured to be disposed within the subject's left ventricle, for someapplications, blood-pressure-measurement tube 210 and the techniquesdescribed herein for use with blood-pressure-measurement tube 210 areused with a ventricular assist device that includes a blood pumpelsewhere, e.g., within the subject's aorta. For some applicationsgenerally similar techniques are used with a right ventricular assistdevice. For example, device 20 may be inserted into the right ventricleand used to pump blood from the right ventricle to the pulmonary artery.For some such applications, the blood-pressure measurement tubes areused to measure pressure in the right ventricle and/or the pulmonaryartery. For some applications, a generally similar device to device 20is used as a cardiac assist device by being used to pump blood in anantegrade direction from the right atrium to the right ventricle, fromthe vena cava to the right ventricle, from the right atrium to thepulmonary artery, and/or from the vena cava to the pulmonary artery. Forsome such applications, the blood-pressure measurement tubes are used tomeasure pressure in the right ventricle, the vena cava, the rightatrium, and/or the pulmonary artery.

In general, the scope of the present invention includes applying any ofthe apparatus and methods that are described herein to a rightventricular assist device, mutatis mutandis. The right-ventricularassist device typically has a generally similar configuration to thatdescribed herein and is used to pump blood from the right ventricle tothe pulmonary artery, with tube 24 passing through the pulmonarysemilunar valve. For some applications, components of device 20 areapplicable to different types of blood pumps. For example, aspects ofthe present invention may be applicable to a pump that is used to pumpblood from the vena cava and/or the right atrium into the rightventricle, from the vena cava and/or the right atrium into the pulmonaryartery, and/or from the renal veins into the vena cava. Such aspects mayinclude features of pump portion 27, impeller 50, features of drivecable 130, apparatus and methods for measuring blood pressure, apparatusand methods for measuring flow, etc.

For some applications, generally similar techniques to those describedwith reference to blood-pressure-measurement tube 210 are performedusing an electrical wire that extends from within blood-pump tube 24(and that typically extends from outside the subject's body) to theouter surface of tube 24, such that at least a tip of the wire is inelectrical communication with the subject's bloodstream outside of tube24. The subject's blood pressure outside tube 24 (e.g., the subject'sventricular blood pressure and/or the subject's aortic blood pressure)is measured by detecting an electrical parameter using the portion ofthe wire that is in electrical communication with the subject'sbloodstream outside tube 24.

Reference is now made to FIGS. 17A, 17B, and 17C, which are schematicillustrations of outer tube 142 of ventricular assist device 20, theouter tube including a pitot tube 225 that is configured to measureblood flow through tube 24 of the device, in accordance with someapplications of the present invention. The portion of outer tube 142shown in FIGS. 17A-C is typically disposed within tube 24. For someapplications, a flow obstacle 226 (which is typically funnel shaped) isconfigured to create a stagnation region near a stagnation pressure tap227. For some applications, flow straighteners 228 are added to theouter surface of tube 142, in order remove any swirling component of theflow (which does not contribute to the axial flow rate), as shown inFIG. 17A. Alternatively, the stagnation pressure tap is disposedsufficiently proximally within funnel-shaped flow obstacle 226 that theflow obstacle itself acts to remove the swirling components of the flow,prior to the blood reaching the stagnation pressure tap, as shown inFIG. 17B. For some applications, the stagnation pressure tap includes ashort tube 233 that protrudes from outer tube 142 within funnel-shapedflow obstacle 226, such that the opening of short tube 233 faces thedirection of axial blood flow through tube 24. Outer tube 142additionally defines opening 219, which is generally as describedhereinabove, and which functions as a static pressure tap 229. Thepressure within stagnation pressure tap 227 and within static pressuretap 229 is measured using pressure sensors, e.g., pressure sensors thatare disposed outside the subject's body, as described hereinabove withreference to FIGS. 16A-D.

In some applications, flow through tube 24 is calculated based upon thepressure measurements. For example, flow through tube 24 may becalculated using the following equation:

$Q = {C \cdot A \cdot \sqrt{\frac{2\Delta P}{\rho}}}$

in which:

Q is the flow through tube 24,

C is a calibration constant that is empirically determined and accountsfor factors such as impeller velocity and the geometries of pressuretaps 227 and 229,

A is the cross-sectional area of tube 24 (not including the area thatouter tube 142 occupies),

ΔP is the difference between the stagnation pressure (measured viapressure tap 227), and the static pressure (measured via pressure tap229)

ρ is the fluid density of blood.

Reference is now made to FIG. 18 , which is a schematic illustration ofventricular assist device 20, distal tip portion 120 of the device,being a radially-expandable atraumatic distal tip portion, in accordancewith some applications of the present invention. As describedhereinabove, the ventricular assist device typically includes tube 24,which traverses the subject's aortic valve, such that a proximal portionof the tube is disposed within the subject's aorta, and a distal portionof the tube is disposed within the subject's left ventricle. Tube 24defines one or more blood inlet openings 108 within the distal portionof the tube, and one or more blood outlet openings 109 within theproximal portion of the tube. A blood pump of the ventricular assistdevice, which is configured to be disposed within tube 24, pumps bloodfrom the left ventricle into tube 24 through the one or more blood inletopenings, and out of tube 24 into the aorta through the one or moreblood outlet openings. Typically, radially-expandable atraumatic distaltip portion 120 is disposed within the subject's left ventricle distallywith respect to the one or more blood inlet openings. The distal tipportion is configured to be inserted into the left ventricle in aradially-constrained configuration. Typically, at least a portion of thedistal tip portion is disposed inside delivery catheter 143 (shown inFIG. 1B, for example) during insertion of the distal tip portion intothe left ventricle, and the delivery catheter maintains the distal tipportion in the radially-constrained configuration. The distal tipportion is configured to assume a non-radially-constrained configurationwithin the subject's left ventricle, in which at least a portion 232 ofthe distal tip portion is radially expanded relative to theradially-constrained configuration of the distal tip.

For some applications, radially-expandable atraumatic distal tip portion120 includes a frame 234 made of a shape-memory material (such asnitinol), which is shape set, such that the frame radially expands uponbeing released from the delivery catheter. Typically, the frame iscovered with a biocompatible blood-impermeable material 236, such aspolyurethane, polyester, and/or silicone, which is typically configuredto form a continuous surface that covers the frame. For someapplications, the distal tip portion additionally includes an atraumaticdistal tip 238, which may have a similar shape to distal tip portion120, as described hereinabove with reference to FIG. 6C and/orhereinbelow with reference to FIG. 21B.

Radially-expandable atraumatic distal tip portion 120 is typicallyconfigured such that, in the non-radially-constrained configuration ofthe distal tip portion, radially-expandable portion 232 of the distaltip portion separates one or more blood inlet openings 108 from innerstructures of the left ventricle in three dimensions. In this manner,radially-expandable portion 232 of the distal tip portion separates oneor more blood inlet openings 108 from the interventricular septum,chordae tendineae, papillary muscles, and/or the apex of the leftventricle. For some applications, the radially-expandable portion 232 ofthe distal tip portion is shaped such as to direct blood flow from theleft ventricle into the one or more blood inlet openings, as indicatedby arrows 240 in FIG. 18 .

Reference is now made to FIGS. 19A-19B, which are schematicillustrations of ventricular assist device 20, the ventricular assistdevice distal tip portion 120 of the device, being a radially-expandableatraumatic distal tip portion, in accordance with some applications ofthe present invention. Reference is also made to FIGS. 20A-20B, whichare schematic illustrations of ventricular assist device 20, theventricular assist device distal tip portion 120 of the device, being aradially-expandable atraumatic distal tip portion, in accordance withsome alternative applications of the present invention. FIGS. 19A and20A show the distal tip portion in its radially-constrainedconfiguration, while disposed at least partially inside deliverycatheter 143, and FIGS. 19B and 20B show the distal tip portion in itsnon-radially-constrained configuration. In general, distal tip portion120 as shown in FIGS. 19A-B and 20A-B has generally similarfunctionality to that described hereinabove with reference to distal tipportion 120 as shown in FIG. 18 .

As described hereinabove, typically, at least a portion of distal tipportion 120 is disposed inside delivery catheter 143 during insertion ofthe distal tip into the left ventricle, and the delivery cathetermaintains the distal tip portion in the radially-constrainedconfiguration, as shown in FIGS. 19A and 20A. For some applications, thedistal tip portion is configured such that, when the delivery cathetermaintains the distal tip portion in the radially-constrainedconfiguration, a distal region 244 of the distal tip portion protrudesfrom a distal end of the delivery catheter. Typically, at least in theradially-constrained configuration of the distal tip portion, the distalregion is at least semi-rigid, and is shaped to converge radially in thelongitudinal direction toward a distal end 246 of the distal tipportion. Typically, the delivery catheter is inserted into the subject'svasculature via a puncture. For some applications, theradially-converging semi-rigid distal region of the distal tip portionis configured to act as a dilator, by dilating the puncture duringinsertion of the delivery catheter via the puncture. In this manner, thedelivery catheter and components of the ventricular assist device thatare disposed within the delivery catheter can be inserted into thepuncture without requiring pre-dilation of the puncture, and withoutrequiring a separate introducer device, for facilitating insertion ofthe delivery catheter through the puncture. For some applications, thedistal region is configured to allow percutaneous insertion of thecatheter into a punctured vessel, by placing a first guidewire throughthe distal region of the distal tip portion. Subsequently, the distalregion is used to guide the catheter along an arched anatomy (e.g., theaortic arch) by tracking the course and shape of a second guidewire thatis less stiff than the first guidewire. For some such applications,delivery catheter 143 itself acts as an introducer. Typically, thedelivery catheter has an inner diameter of less than 9 mm. For example,the delivery catheter may be an 8 French catheter. For someapplications, the delivery catheter is inserted through the puncture viaa short introducer device.

For some applications, distal tip portion 120 is configured such that inthe non-radially-constrained configuration of the distal tip portion,distal end 246 of the distal tip portion is enveloped withinradially-expandable portion 232 of the distal tip portion. For someapplications, the distal end is retracted proximally, such that thedistal end is enveloped within the radially-expandable portion. Forexample, the distal tip portion may include a spring 249 and/or anelastomeric material that is configured to retract the distal end of thedistal tip portion, as shown in the transition from FIG. 19A to FIG.19B. For some applications, the distal end inverts, such that the distalend becomes enveloped within the radially-expandable portion of thedistal tip portion. For example, the transition from FIG. 20A to 20Bshows distal end 246 of distal tip portion 120 inverting, as indicatedby arrows 264. For some applications, by the distal end becomingenveloped within the radially-expandable portion, the distal tip isprevented from becoming entangled within the chordae tendineae, and/oris prevented from causing trauma to an internal structure of the leftventricle.

Referring to FIG. 19B, for some applications, the distal tip portionincludes a plurality of longitudinal struts 248, which are shape set tocurve radially outwardly. Typically, the struts are made of ashape-memory material, such as nitinol. For some applications, thestruts are covered with a biocompatible blood-impermeable material 250,such as polyurethane, polyester, and/or silicone, which is typicallyconfigured to form a continuous surface that covers the struts.Referring to FIG. 20B, for some applications, the distal tip portionincludes a braided shape-memory material 260. For some applications, thebraided shape-memory material is at least partially covered with abiocompatible blood-impermeable material 262, such as polyurethane,polyester, and/or silicone, which is typically configured to form acontinuous surface that covers the braided shape-memory material.Alternatively, the braided shape-memory material is not covered.

Reference is now made to FIGS. 21A, 21B, 21C, and 21D, which areschematic illustrations of distal tip portion 120 of ventricular assistdevice 20, the distal tip portion being configured to be atraumatic, inaccordance with some applications of the present invention. As shown inFIG. 21A, for some applications, the distal tip portion includes a J-tip270 at its distal end. As shown in FIG. 21B, for some applications, thedistal tip portion includes a bulbous tip 272 at its distal end. Asshown in FIGS. 21A and 21B, for some applications, proximal to the J-tipor the bulbous tip, the distal tip portion is externally shaped todefine a frustum 274. Typically, a proximal end 276 of the frustum actsas a stopper for preventing advancement of delivery catheter 143 pastthe proximal end, in a generally similar manner to that described withrespect to flared portion 124, with reference to FIG. 6C.

For some applications, the tip portion has a straightened configurationin which the tip portion is shaped to define a frustum that extends fromthe proximal end of the frustum until the distal tip of the distal tipportion. For example, a guidewire (such as guidewire 10) that isinserted through lumen 122 (shown in FIGS. 6A-C) defined by the tipportion may maintain the tip portion in its straightened configuration.For some such applications, the tip portion has a non-constrainedconfiguration (which the tip portion is configured to assume inside theventricle (e.g., due to the guidewire being removed from inside the tipportion)), in which a distal portion of the frustum is shaped as aJ-tip, as shown in FIG. 21A.

As shown in FIG. 21C, for some applications, the outer surface of thedistal tip portion includes an inflatable portion 278 (e.g., a balloon),which is configured to be inflated when the distal tip portion isdisposed inside the subject's left ventricle. For some suchapplications, an inflation lumen for inflating the inflatable portion isconfigured to pass through outer tube 142, and to then pass along theouter surface of tube 24, and to the inflatable portion of the distaltip portion. For example, the inflation lumen may be configured in agenerally similar manner to blood-pressure measurement tube 210 as shownin FIG. 16D, but may continue to run along the outer surface of tube 24until the distal end of the tube, and then continue to the inflatableportion of the distal tip portion. For some applications, the distal endof the distal tip portion includes a rounded portion 280. As describedhereinabove, typically, the distal tip portion includes a hemostasisvalve 152 at its distal end.

As shown in FIG. 21D, for some applications, the outer surface of thedistal tip portion includes a radially expandable portion 282 (e.g., aradially expandable mesh, as shown, and/or a radially-expandable frame),which is configured to self-expand when the distal tip portion isdisposed inside the subject's left ventricle.

Atraumatic distal tip portion 120, as shown in FIGS. 21C and 21D, istypically configured such that, in the inflated or radially-expandedconfiguration of the distal tip portion, the inflated portion or theradially expanded portion of the distal tip portion separates one ormore blood inlet openings 108 from inner structures of the leftventricle in three dimensions. In this manner, the inflated portion orthe radially expanded portion of the distal tip portion separates one ormore blood inlet openings 108 from the interventricular septum, chordaetendineae, papillary muscles, and/or the apex of the left ventricle. Forsome applications, the inflated portion or the radially expanded portionof the distal tip portion is shaped such as to direct blood flow fromthe left ventricle into the one or more blood inlet openings, asdescribed hereinabove with reference to distal tip portion 120 as shownin FIG. 18 .

Reference is now made to FIGS. 22A and 22B, which are schematicillustrations of distal tip portion 120 of ventricular assist device 20,respectively, in an axially-stiffened configuration and anon-axially-stiffened configuration, in accordance with someapplications of the present invention. As described hereinabove, forsome applications, the distal tip portion is configured such that, whenthe delivery catheter maintains the distal tip portion in theradially-constrained configuration, a distal region 244 of the distaltip portion protrudes from a distal end of the delivery catheter.Typically, at least in the axially-stiffened configuration of the distaltip portion, the distal region is at least semi-rigid, and is shaped toconverge radially in the longitudinal direction toward a distal end 246of the distal tip portion. Typically, the delivery catheter is insertedinto the subject's vasculature via a puncture. Further typically, thedistal tip portion defines lumen 122, through which guidewire 10 isinserted, as described hereinabove. For some applications, theradially-converging semi-rigid distal region of the distal tip portionis configured to act as a dilator, by dilating the puncture duringinsertion of the delivery catheter via the puncture. In this manner, thedelivery catheter and components of the ventricular assist device thatare disposed within the delivery catheter can be inserted into thepuncture without requiring pre-dilation of the puncture, and withoutrequiring a separate introducer device, for facilitating insertion ofthe delivery catheter through the puncture. For some applications, thedistal region is configured to allow percutaneous insertion of thecatheter into a punctured vessel, by placing a first guidewire throughthe distal region of the distal tip portion. Subsequently, the distalregion is used to guide the catheter along an arched anatomy (e.g., theaortic arch) by tracking the course and shape of a second guidewire thatis less stiff than the first guidewire. For some such applications,delivery catheter 143 itself acts as an introducer. Typically, thedelivery catheter has an inner diameter of less than 9 mm. For example,the delivery catheter may be an 8 French catheter. For someapplications, the delivery catheter is inserted through the puncture viaa short introducer device.

For some applications, the distal tip portion is made of a flexiblematerial (such as silicone) with a spring 290 disposed around lumen 122.During insertion of the ventricular assist device into the subject'sbody, a rigid or semi-rigid stiffening element 292 (e.g., a rigid orsemi-rigid tube) is placed inside distal region 244 of the distal tipportion, such as to stiffen the distal region. This configuration isshown in FIG. 22A. Subsequently, the stiffening element is retracted,such that the distal region of the distal tip portion becomes atraumatic(e.g., springy and flexible), as shown in FIG. 22B.

Reference is now made to FIGS. 23A and 23B, which are schematicillustrations of distal tip portion 120 of ventricular assist device 20,respectively, in a radially-constrained configuration and anon-radially-constrained configuration, in accordance with someapplications of the present invention. For some applications, distalregion 144 of the distal tip portion is shaped as a cone with slits 294(e.g., two slits) in the cone. During insertion of the ventricularassist device into the subject's body, the distal region is maintainedin its conical shape by delivery catheter 143. This configuration isshown in FIG. 23A. Subsequently, when the delivery catheter isretracted, the distal region is configured to form a two-dimensionalcircular or elliptical shape, by splitting into two semi-circles 296 orsemi-ellipses around the slits, as shown in FIG. 23B. In theconfiguration shown in FIG. 23B, the distal tip portion is typicallyconfigured to be atraumatic and to separate the one or more blood inletopenings 108 from inner structures of the left ventricle in twodimensions. In this manner, the distal tip portion separates one or moreblood inlet openings 108 from the interventricular septum, chordaetendineae, papillary muscles, and/or the apex of the left ventricle.

Reference is now made to FIGS. 24A and 24B, which are schematicillustrations of distal tip portion 120 of ventricular assist device 20,respectively, in a radially-constrained configuration and anon-radially-constrained configuration, in accordance with someapplications of the present invention. For some applications, distalregion 244 of the distal tip portion is shaped as a cone with slits 294(e.g., four slits) in the cone. During insertion of the ventricularassist device into the subject's body, the distal region is maintainedin its conical shape by delivery catheter 143. This configuration isshown in FIG. 24A. Subsequently, when the delivery catheter isretracted, the distal region is configured to form a three-dimensionalbasket shape, by splitting into four arms 298 around the slits, as shownin FIG. 24B. (It is noted that the fourth arm is hidden from view inFIG. 24B.) In the configuration shown in FIG. 24B, the distal tipportion is typically configured to be atraumatic and to separate the oneor more blood inlet openings 108 from inner structures of the leftventricle in three dimensions. In this manner, the distal tip portionseparates one or more blood inlet openings 108 from the interventricularseptum, chordae tendineae, papillary muscles, and/or the apex of theleft ventricle.

For some applications, distal tip portion 120 has a pointed distalregion 244, the diameter of the distal tip portion at the proximal endof the distal region being approximately equal to that of deliverycatheter 143. Typically, pointed distal region 244 has a length of lessthan half (e.g., less than a quarter) of the total length of the distaltip portion. Further typically, the flexibility of the pointed distalregion is greater than that of a proximal region of the distal tipportion. Typically, the distal region is configured to be straightenedto a generally conical shape when a sufficiently stiff guidewire isinserted into it. For some applications, the distal region is configuredto curl to a J-shape, in the absence of any external forces acting onthe distal region (e.g., as shown in FIG. 21A).

Typically, the distal region of the distal tip portion acts as a dilatorfor delivery catheter 143, to allow percutaneous insertion of thecatheter into a punctured vessel, by placing a first guidewire throughthe distal region of the distal tip portion. Subsequently, the distaltip portion is used to guide the catheter along an arched anatomy (e.g.,the aortic arch) by tracking the course and shape of a second guidewirethat is less stiff than the first guidewire. For some applications, thedistal region of the distal tip portion is configured to curl, when thesecond guidewire is withdrawn, as described hereinabove.

For some applications, features of distal tip portion 120 described withreference to FIGS. 18-24B, as well as techniques for practicingtherewith, are combined with features described with reference to tipportion 120, described hereinabove with reference to FIGS. 6A-C, and/or13, as well as techniques for practicing therewith.

Reference is now made to FIG. 25A, which is a schematic illustration offirst portion 160A and second portion 160B of a coupling elementconfigured to facilitate radial constriction (e.g., during crimping) ofan impeller (e.g., impeller 50 described hereinabove) independently ofother components of a ventricular assist device, in accordance with someapplications of the present invention. First and second portions 160Aand 160B are configured to become engaged with each other. The firstportion is disposed on the impeller, and the second portion is disposedon frame 34, e.g., on distal bearing 118 of frame 34. It is noted thatonly certain portions of the impeller are show in FIG. 25A, forillustrative purposes.

Reference is also made to FIGS. 25B and 25C, which are schematicillustrations of respective stages of the crimping of the impeller, inaccordance with some applications of the present invention. For someapplications, prior to crimping an outer portion of the ventricularassist device (e.g., frame 34 of left ventricular assist device 20, asshown), the impeller is radially constricted, by engaging portions 160Aand 160B with each other and axially elongating the impeller, such as toradially constrict the impeller. Subsequently, the outer portion of theleft ventricular assist device is radially constricted. For someapplications, crimping the impeller in this manner reduces a likelihoodof the impeller becoming damaged during the crimping of the outerportion of the left ventricular assist device. Subsequently, when theimpeller and the frame are disposed in the subject's left ventricle, thefirst and second portions of the coupling element are decoupled fromeach other, such that the impeller is able to move with respect to frame34.

Alternatively or additionally to the crimping technique shown in FIGS.25A-C, the impeller is configured to become crimped by virtue of onlyone of the ends of the impeller (e.g., the proximal end of the impeller)being coupled to the axial shaft, and the other end (e.g., the distalend) being slidable with respect to the axial shaft, as describedhereinabove. The impeller becomes crimped by the other end of theimpeller sliding along the shaft, such that the impeller becomes axiallyelongated.

Reference is now made to FIG. 26 , which is a schematic illustration ofa stopper 300 configured to prevent distal advancement of impeller 50 ofventricular assist device 20 during withdrawal of the ventricular assistdevice from the subject's body, in accordance with some applications ofthe present invention. As described hereinabove, typically, in order towithdraw the ventricular assist device from the subject's body, deliverycatheter 143 is advanced distally over frame 34 and impeller 50, inorder to cause the frame and the impeller to assume theirradially-constrained configurations. In some cases, there is a riskthat, as the impeller is pushed distally by the delivery catheter, drivecable 130 may snap. For some applications, in the event that the drivecable snaps, then distal advancement of the proximal end of the impellercauses stopper 300 to engage with a shoulder 302, thereby preventingfurther advancement of the proximal end of the impeller. It is notedthat the stopper is configured such that, during regular operation ofthe ventricular assist device (and throughout the axial back-and-forthmotion cycle described hereinabove), the stopper does not engage withshoulder 302.

For some applications (not shown), a plurality of electrodes aredisposed upon a distal portion of a left-ventricular assist device.Computer processor 25 (FIG. 1A) applies a current between the mostdistal electrode, which is typically configured to be disposed near theapex of the heart, and the most proximal electrode, which is typicallyconfigured to be disposed above the aortic valve. Conductance of thatcurrent between each pair of the electrodes is then measured by thecomputer processor. For some applications, the application of thecurrent, and the conductance measurements, are performed using generallysimilar techniques to those described in an article entitled “TheConductance Volume Catheter Technique for Measurement of LeftVentricular Volume in Young Piglets,” by Cassidy et al. (PediatricResearch, Vol. 31, No. 1, 1992, pp. 85-90). For some applications, thecomputer processor is configured to derive the subject's real-timeleft-ventricular pressure-volume loop based upon the conductancemeasurements. For some applications, the computer processor controls arate of rotation of the impeller responsively to the derivedpressure-volume loop.

With regards to all aspects of ventricular assist device 20 describedwith reference to FIGS. 1A-26 , it is noted that, although FIGS. 1A and1B show ventricular assist device 20 in the subject's left ventricle,for some applications, device 20 is placed inside the subject's rightventricle, such that the device traverses the subject's pulmonary valve,and techniques described herein are applied, mutatis mutandis. For someapplications, components of device 20 are applicable to different typesof blood pumps. For example, aspects of the present invention may beapplicable to a pump that is used to pump blood from the vena cavaand/or the right atrium into the right ventricle, from the vena cavaand/or the right atrium into the pulmonary artery, and/or from the renalveins into the vena cava. Such aspects may include features of impeller50, features of pump portion 27, drive cable 130, apparatus and methodsfor measuring blood pressure, etc. Alternatively or additionally, device20 and/or a portion thereof (e.g., impeller 50, even in the absence oftube 24) is placed inside a different portion of the subject's body, inorder to assist with the pumping of blood from that portion. Forexample, device 20 and/or a portion thereof (e.g., impeller 50, even inthe absence of tube 24) may be placed in a blood vessel and may be usedto pump blood through the blood vessel. For some applications, device 20and/or a portion thereof (e.g., impeller 50, even in the absence of tube24) is configured to be placed within the subclavian vein or jugularvein, at junctions of the vein with a lymph duct, and is used toincrease flow of lymphatic fluid from the lymph duct into the vein,mutatis mutandis. Since the scope of the present invention includesusing the apparatus and methods described herein in anatomical locationsother than the left ventricle and the aorta, the ventricular assistdevice and/or portions thereof are sometimes referred to herein (in thespecification and the claims) as a blood pump.

Reference is now made to FIGS. 27A and 27B, which are schematicillustrations of a ventricular assist device 308, the device including avalve 70 to prevent backflow of blood, for example, in the event thatimpeller 50 of the ventricular assist device malfunctions, in accordancewith some applications of the present invention. Unlike ventricularassist device 20 described hereinabove with reference to FIGS. 1A-26 ,ventricular assist device 308 includes an impeller disposed within theaorta, and not in the left ventricle (e.g., as described in WO 18/078615to Tuval, which is incorporated herein by reference). For someapplications, the impeller is configured in a generally similar mannerto impeller 50 described hereinabove. The impeller is disposed at aproximal end of a tube 312 (e.g., a polyester tube), which traverses theaortic valve, and a frame 310 supports the tube in an openconfiguration. FIG. 27A shows the ventricular assist device asconfigured when the impeller of the ventricular assist device isfunctioning normally, such that there is blood flow from left ventricle22 to aorta 30, via tube 312 (which traverses aortic valve 26), theblood flow being indicated by arrows 72.

For some applications, tube 312 includes valve 70 at a region of thetube that is configured to be disposed distally with respect to impeller50 and in the vicinity of the aortic valve, as shown in FIG. 27B. In theevent that, for example, impeller 50 malfunctions, such that there isbackflow of blood via tube 312 (as indicated by blood flow arrows 73 inFIG. 27B), leaflets of valve 70 are configured to close, such that thereis substantially no retrograde blood flow from the aorta to the leftventricle. For some applications (not shown), tube 312 includes valve 70at a proximal end of the tube, which is configured to be disposed in theaorta.

Reference is now made to FIGS. 28A, 28B, and 28C, which are schematicillustrations of ventricular assist device 308, the device including asafety balloon 80 to prevent backflow of blood, for example, in theevent that the impeller of the ventricular assist device malfunctions,in accordance with some applications of the present invention. Unlikeventricular assist device 20 described hereinabove with reference toFIGS. 1A-26 , ventricular assist device 308 includes an impellerdisposed within the aorta, and not in the left ventricle (e.g., asdescribed in WO 18/078615 to Tuval, which is incorporated herein byreference). For some applications, the impeller is configured in agenerally similar manner to impeller 50 described hereinabove. Theimpeller is disposed at a proximal end of tube 312 (e.g., a polyestertube), which traverses the aortic valve, and frame 310 supports the tubein an open configuration. FIG. 28A shows the ventricular assist deviceas configured when the impeller of the ventricular assist device isfunctioning normally, such that there is blood flow from left ventricle22 to aorta 30, via tube 312 (which traverses aortic valve 26), theblood flow being indicated by arrows 72. For some applications,ventricular assist device 308 includes balloon 80 at a region of thetube that is configured to be disposed distally with respect to impeller50 and in the vicinity of the aortic valve, as shown in FIG. 28B. In theevent that, for example, impeller 50 malfunctions, such that there isbackflow of blood via tube 312 (as indicated by blood flow arrows 73 inFIG. 28B), computer processor 25 is configured to inflate the balloon,such that tube 312 becomes occluded and there is substantially noretrograde blood flow from the aorta to the left ventricle.

For some applications, ventricular assist device 308 includes balloon 80at the distal end of tube 312, which is configured to be disposed in theleft ventricle, as shown in FIG. 28C. In the event that, for example,impeller 50 malfunctions, such that there is backflow of blood via tube312 (as indicated by blood flow arrows 73 in FIG. 28C), computerprocessor 25 is configured to inflate the balloon, such that tube 312becomes occluded and there is substantially no retrograde blood flowfrom the aorta to the left ventricle.

The scope of the present invention includes combining any of theapparatus and methods described herein with any of the apparatus andmethods described in one or more of the following applications, all ofwhich are incorporated herein by reference:

-   International Patent Application PCT/IL2017/051273 to Tuval    (published as WO 18/096531), filed Nov. 21, 2017, entitled “Blood    pumps,” which claims priority from U.S. Provisional Patent    Application 62/425,814 to Tuval, filed Nov. 23, 2016;-   International Application No. PCT/IL2017/051158 to Tuval (published    as WO 18/078615), entitled “Ventricular assist device,” filed Oct.    23, 2017, which claims priority from U.S. 62/412,631 to Tuval filed    Oct. 25, 2016, and U.S. 62/543,540 to Tuval, filed Aug. 10, 2017;-   International Patent Application PCT/IL2017/051092 to Tuval    (published as WO 18-061002), filed Sep. 28, 2017, entitled “Blood    vessel tube,” which claims priority from U.S. Provisional Patent    Application 62/401,403 to Tuval, filed Sep. 29, 2016;-   US 2018/0169313 to Schwammenthal, which is the US national phase of    International Patent Application PCT/IL2016/050525 to Schwammenthal    (published as WO 16/185473), filed May 18, 2016, entitled “Blood    pump,” which claims priority from U.S. Provisional Patent    Application 62/162,881 to Schwammenthal, filed May 18, 2015,    entitled “Blood pump;”-   US 2017/0100527 to Schwammenthal, which is the US national phase of    International Patent Application PCT/IL2015/050532 to Schwammenthal    (published as WO 15/177793), filed May 19, 2015, entitled “Blood    pump,” which claims priority from U.S. Provisional Patent    Application 62/000,192 to Schwammenthal, filed May 19, 2014,    entitled “Blood pump;”.-   U.S. Pat. No. 10,039,874 to Schwammenthal, which is the US national    phase of International Patent Application PCT/IL2014/050289 to    Schwammenthal (published as WO 14/141284), filed Mar. 13, 2014,    entitled “Renal pump,” which claims priority from (a) U.S.    Provisional Patent Application 61/779,803 to Schwammenthal, filed    Mar. 13, 2013, entitled “Renal pump,” and (b) U.S. Provisional    Patent Application 61/914,475 to Schwammenthal, filed Dec. 11, 2013,    entitled “Renal pump;”-   U.S. Pat. No. 9,764,113 to Tuval, issued Sep. 19, 2017, entitled    “Curved catheter,” which claims priority from U.S. Provisional    Patent Application 61/914,470 to Tuval, filed Dec. 11, 2013,    entitled “Curved catheter;” and-   U.S. Pat. No. 9,597,205 to Tuval, which is the US national phase of    International Patent Application PCT/IL2013/050495 to Tuval    (published as WO 13/183060), filed Jun. 6, 2013, entitled    “Prosthetic renal valve,” which claims priority from U.S.    Provisional Patent Application 61/656,244 to Tuval, filed Jun. 6,    2012, entitled “Prosthetic renal valve.”

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather, the scope of the present inventionincludes both combinations and subcombinations of the various featuresdescribed hereinabove, as well as variations and modifications thereofthat are not in the prior art, which would occur to persons skilled inthe art upon reading the foregoing description.

The invention claimed is:
 1. An apparatus comprising: a blood pumpcomprising: an impeller; a frame configured to be disposed around theimpeller; a motor configured to drive the impeller to pump blood byrotating the impeller, the entire impeller being configured to undergoaxial back-and-forth motion relative to the frame, in response tochanges in pressure against which the impeller is pumping; a sensorconfigured to detect the axial back-and-forth motion of the impeller,and to generate a sensor signal that is indicative of the detected axialback-and-forth motion of the impeller; and a computer processorconfigured to receive the sensor signal and to generate an output inresponse thereto.
 2. The apparatus according to claim 1, wherein theimpeller is configured to undergo the axial back-and-forth motion inresponse to cyclical changes in pressure against which the impeller ispumping.
 3. The apparatus according to claim 1, wherein the computerprocessor is configured to generate an output indicating a cardiac cycleof the subject, in response to receiving the sensor signal.
 4. Theapparatus according to claim 1, wherein the computer processor isconfigured to change a rate of rotation of the impeller, at leastpartially based upon the sensor signal.
 5. The apparatus according toclaim 1, wherein the blood pump comprises a left ventricular assistdevice, and wherein the impeller is configured to pump blood from a leftventricle of the subject to an aorta of the subject.
 6. The apparatusaccording to claim 5, wherein the impeller is configured to undergo theaxial back-and-forth motion in response to cyclical changes in apressure difference between the subject's left ventricle and thesubject's aorta.
 7. The apparatus according to claim 5, wherein thecomputer processor is configured to determine left-ventricular pressureof the subject, at least partially based upon the sensor signal.
 8. Theapparatus according to claim 7, wherein the computer processor isconfigured to change a rate of rotation of the impeller, at leastpartially based upon the determined left-ventricular pressure.
 9. Theapparatus according to claim 8, wherein the computer processor isconfigured to reduce the rate of rotation of the impeller, in responseto determining that the subject's left-ventricular pressure hasdecreased.
 10. The apparatus according to claim 1, wherein: the bloodpump further comprises a magnet, the impeller being coupled to themagnet such that the axial back-and-forth motion of the impeller causesthe magnet to undergo axial back-and-forth motion, and the sensorconfigured to detect magnetic flux generated by the magnet, and togenerate the sensor signal in response thereto.
 11. The apparatusaccording to claim 10, wherein the magnet is configured to be disposedoutside the subject's body, the blood pump further comprising a drivecable that is configured to extend from the magnet to the impeller, suchthat the impeller is coupled to the magnet via the drive cable.
 12. Theapparatus according to claim 10, wherein the impeller is configured toundergo the axial back-and-forth motion in response to cyclical changesin pressure against which the impeller is pumping.
 13. The apparatusaccording to claim 10, wherein the computer processor is configured tochange a rate of rotation of the impeller, at least partially based uponthe sensor signal.
 14. The apparatus according to claim 10, wherein theblood pump comprises a left ventricular assist device, and wherein theimpeller is configured to pump blood from a left ventricle of thesubject to an aorta of the subject.
 15. The apparatus according to claim14, wherein the impeller is configured to undergo the axialback-and-forth motion in response to cyclical changes in a pressuredifference between the subject's left ventricle and the subject's aorta.16. The apparatus according to claim 14, wherein the computer processoris configured to determine left-ventricular pressure of the subject, atleast partially based upon the sensor signal.
 17. The apparatusaccording to claim 16, wherein the computer processor is configured tochange a rate of rotation of the impeller, at least partially based uponthe determined left-ventricular pressure.
 18. The apparatus according toclaim 17, wherein the computer processor is configured to reduce therate of rotation of the impeller, in response to determining that thesubject's left-ventricular pressure has decreased.
 19. A methodcomprising: placing an impeller of a blood pump into a body of a subjectwith a frame disposed around the impeller; and driving the impeller topump blood within the subject's body, placement of the impeller insidethe subject's body being such that the entire impeller is allowed toundergo axial back-and-forth motion relative to the frame, in responseto changes in pressure against which the impeller pumps; detecting anindication of the axial back-and-forth motion of the impeller; andgenerating an output in response to the detected indication of the axialback-and-forth motion of the impeller.
 20. The method according to claim19, wherein: placing the impeller inside the subject's body comprisesplacing the impeller inside the subject's body with a magnet coupled tothe impeller such that the axial back-and-forth motion of the impellercauses the magnet to undergo axial motion, and detecting the indicationof the axial motion of the impeller comprises detecting magnetic fluxgenerated by the magnet.
 21. The method according to claim 19, whereinplacing the impeller inside the subject's body comprises placing theimpeller inside a left ventricle of the subject, such that the impelleris allowed to undergo the axial back-and-forth motion, in response tocyclical changes in a pressure difference between the subject's leftventricle and an aorta of the subject.